Martin, thanks for your suggestion to check the kernel log.  When I did
I found that the device appeared to have actually mounted.

I understand the details may be important so the below is the entry for
the four seconds which are relevant:

2026-06-22T13:54:48.020862-05:00 local kernel: usb 2-1.6: new high-speed
USB device number 4 using ehci-pci
2026-06-22T13:54:48.116860-05:00 local kernel: usb 2-1.6: New USB device
found, idVendor=1f75, idProduct=0611, bcdDevice= 0.06
2026-06-22T13:54:48.116870-05:00 local kernel: usb 2-1.6: New USB device
strings: Mfr=4, Product=5, SerialNumber=6
2026-06-22T13:54:48.116871-05:00 local kernel: usb 2-1.6: Product: XT-U33502
2026-06-22T13:54:48.116872-05:00 local kernel: usb 2-1.6: SerialNumber:
20210105
2026-06-22T13:54:48.140823-05:00 local kernel: usb-storage 2-1.6:1.0:
USB Mass Storage device detected
2026-06-22T13:54:48.140835-05:00 local kernel: scsi host6: usb-storage
2-1.6:1.0
2026-06-22T13:54:48.140835-05:00 local kernel: usbcore: registered new
interface driver usb-storage
2026-06-22T13:54:48.148813-05:00 local kernel: usbcore: registered new
interface driver uas
2026-06-22T13:54:49.148836-05:00 local kernel: scsi host6: scsi scan:
INQUIRY result too short (5), using 36
2026-06-22T13:54:49.148852-05:00 local kernel: scsi 6:0:0:0:
Direct-Access     SATA SSD                       PQ: 0 ANSI: 0
2026-06-22T13:54:49.148854-05:00 local kernel: sd 6:0:0:0: Attached scsi
generic sg4 type 0
2026-06-22T13:54:49.148855-05:00 local kernel: sd 6:0:0:0: [sdc]
500118192 512-byte logical blocks: (256 GB/238 GiB)
2026-06-22T13:54:49.148857-05:00 local kernel: sd 6:0:0:0: [sdc] Write
Protect is off
2026-06-22T13:54:49.148858-05:00 local kernel: sd 6:0:0:0: [sdc] Mode
Sense: 3b 00 00 00
2026-06-22T13:54:49.152834-05:00 local kernel: sd 6:0:0:0: [sdc] No
Caching mode page found
2026-06-22T13:54:49.152843-05:00 local kernel: sd 6:0:0:0: [sdc]
Assuming drive cache: write through
2026-06-22T13:54:49.184813-05:00 local kernel:  sdc: sdc1 sdc2 sdc3
2026-06-22T13:54:49.184826-05:00 local kernel: sd 6:0:0:0: [sdc]
Attached SCSI disk
2026-06-22T13:55:49.648848-05:00 local kernel: usb 2-1.6: reset
high-speed USB device number 4 using ehci-pci
2026-06-22T13:56:51.072860-05:00 local kernel: usb 2-1.6: reset
high-speed USB device number 4 using ehci-pci
2026-06-22T13:56:51.180857-05:00 local kernel: EXT4-fs (sdc3): mounted
filesystem 76a006eb-b544-43ec-84c7-f06b1768761c r/w with ordered data
mode. Quota mode: none.

From /var/log/user.log I found:

2026-06-22T13:54:48.120782-05:00 local mtp-probe: checking bus 2, device
4: "/sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.6"
2026-06-22T13:54:48.121121-05:00 local mtp-probe: bus: 2, device: 4 was
not an MTP device
2026-06-22T13:54:48.149406-05:00 local mtp-probe: checking bus 2, device
4: "/sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.6"
2026-06-22T13:54:48.149578-05:00 local mtp-probe: bus: 2, device: 4 was
not an MTP device
2026-06-22T13:54:49.228424-05:00 local org.kde.kded.smart: Detected
locale "C" with character encoding "ANSI_X3.4-1968", which is not
UTF-8.#012Qt depends on a UTF-8 locale, and has switched to "C.UTF-8"
instead.#012If this causes problems, reconfigure your locale. See the
locale(1) manual#012for more information.

Checking, I confirmed it did mount (only as
76a006eb-b544-43ec-84c7-f06b1768761c - a UUID rather than a friendly
name under /media/leroy - the expected location), the error message is
at least somewhat erroneous.  The UUID has 755 and root:root ownership
although I tried to mount it as a regular user.  Not surprisingly, the
mounted device had limited access as the user (me) and no option to
unmount it.

I unmounted the above as root using umount <UUID> from /media/leroy. 
Next I tried the 1TB disk using the same adapter and got audible
notification that it was recognized, the kernel log shows:

2026-06-22T14:43:39.708820-05:00 local kernel: EXT4-fs (sdc3):
unmounting filesystem 76a006eb-b544-43ec-84c7-f06b1768761c.
2026-06-22T14:44:03.164822-05:00 local kernel: usb 2-1.6: USB
disconnect, device number 4
2026-06-22T14:44:21.388860-05:00 local kernel: usb 2-1.6: new high-speed
USB device number 5 using ehci-pci
2026-06-22T14:44:21.484822-05:00 local kernel: usb 2-1.6: New USB device
found, idVendor=1f75, idProduct=0611, bcdDevice= 0.06
2026-06-22T14:44:21.484833-05:00 local kernel: usb 2-1.6: New USB device
strings: Mfr=4, Product=5, SerialNumber=6
2026-06-22T14:44:21.484834-05:00 local kernel: usb 2-1.6: Product: XT-U33502
2026-06-22T14:44:21.484835-05:00 local kernel: usb 2-1.6: SerialNumber:
20210105
2026-06-22T14:44:21.484836-05:00 local kernel: usb-storage 2-1.6:1.0:
USB Mass Storage device detected
2026-06-22T14:44:21.484836-05:00 local kernel: scsi host6: usb-storage
2-1.6:1.0
2026-06-22T14:44:22.496849-05:00 local kernel: scsi host6: scsi scan:
INQUIRY result too short (5), using 36
2026-06-22T14:44:22.496865-05:00 local kernel: scsi 6:0:0:0:
Direct-Access     Inland S ATA SSD               PQ: 0 ANSI: 0
2026-06-22T14:44:22.496868-05:00 local kernel: sd 6:0:0:0: Attached scsi
generic sg4 type 0
2026-06-22T14:44:22.496870-05:00 local kernel: sd 6:0:0:0: [sdc]
2000409264 512-byte logical blocks: (1.02 TB/954 GiB)
2026-06-22T14:44:22.500838-05:00 local kernel: sd 6:0:0:0: [sdc] Write
Protect is off
2026-06-22T14:44:22.500847-05:00 local kernel: sd 6:0:0:0: [sdc] Mode
Sense: 3b 00 00 00
2026-06-22T14:44:22.500849-05:00 local kernel: sd 6:0:0:0: [sdc] No
Caching mode page found
2026-06-22T14:44:22.500850-05:00 local kernel: sd 6:0:0:0: [sdc]
Assuming drive cache: write through
2026-06-22T14:44:22.536819-05:00 local kernel:  sdc: sdc1 sdc2 sdc3 sdc4
2026-06-22T14:44:22.536833-05:00 local kernel: sd 6:0:0:0: [sdc]
Attached SCSI disk

And /var/log/user.log contained:

2026-06-22T14:44:21.487543-05:00 local mtp-probe: checking bus 2, device
5: "/sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.6"
2026-06-22T14:44:21.487954-05:00 local mtp-probe: bus: 2, device: 5 was
not an MTP device
2026-06-22T14:44:21.492927-05:00 local mtp-probe: checking bus 2, device
5: "/sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.6"
2026-06-22T14:44:21.493107-05:00 local mtp-probe: bus: 2, device: 5 was
not an MTP device
2026-06-22T14:44:22.593706-05:00 local org.kde.kded.smart: Detected
locale "C" with character encoding "ANSI_X3.4-1968", which is not
UTF-8.#012Qt depends on a UTF-8 locale, and has switched to "C.UTF-8"
instead.#012If this causes problems, reconfigure your locale. See the
locale(1) manual#012for more information.

Nothing was mounted on /media/leroy or anywhere else for that matter.

Finally, to get a reference, I mounted a 128GB USB stick using KDE's
Disks and Devices.  The kernel log follows:

2026-06-22T14:51:28.888847-05:00 local kernel: usb 2-1.6: USB
disconnect, device number 5
2026-06-22T14:52:01.440860-05:00 local kernel: usb 2-1.6: new high-speed
USB device number 6 using ehci-pci
2026-06-22T14:52:01.544845-05:00 local kernel: usb 2-1.6: New USB device
found, idVendor=13fe, idProduct=6700, bcdDevice= 1.10
2026-06-22T14:52:01.544859-05:00 local kernel: usb 2-1.6: New USB device
strings: Mfr=1, Product=2, SerialNumber=3
2026-06-22T14:52:01.544861-05:00 local kernel: usb 2-1.6: Product: USB
DISK 3.0
2026-06-22T14:52:01.544863-05:00 local kernel: usb 2-1.6: Manufacturer:
2026-06-22T14:52:01.544873-05:00 local kernel: usb 2-1.6: SerialNumber:
071C3BE60F8A2D40
2026-06-22T14:52:01.544874-05:00 local kernel: usb-storage 2-1.6:1.0:
USB Mass Storage device detected
2026-06-22T14:52:01.544875-05:00 local kernel: scsi host6: usb-storage
2-1.6:1.0
2026-06-22T14:52:02.556832-05:00 local kernel: scsi 6:0:0:0:
Direct-Access              USB DISK 3.0     PMAP PQ: 0 ANSI: 6
2026-06-22T14:52:02.556847-05:00 local kernel: sd 6:0:0:0: Attached scsi
generic sg4 type 0
2026-06-22T14:52:02.948841-05:00 local kernel: sd 6:0:0:0: [sdc]
242075648 512-byte logical blocks: (124 GB/115 GiB)
2026-06-22T14:52:02.948861-05:00 local kernel: sd 6:0:0:0: [sdc] Write
Protect is off
2026-06-22T14:52:02.948864-05:00 local kernel: sd 6:0:0:0: [sdc] Mode
Sense: 45 00 00 00
2026-06-22T14:52:02.952854-05:00 local kernel: sd 6:0:0:0: [sdc] Write
cache: disabled, read cache: enabled, doesn't support DPO or FUA
2026-06-22T14:52:02.984831-05:00 local kernel:  sdc: sdc1
2026-06-22T14:52:02.984845-05:00 local kernel: sd 6:0:0:0: [sdc]
Attached SCSI removable disk

KDE had a "Mount and open" option which I selected and it mounted as
/media/leroy/'USB DISK'.  The only additional kernel log message was:

2026-06-22T14:53:33.172841-05:00 local kernel: FAT-fs (sdc1): Volume was
not properly unmounted. Some data may be corrupt. Please run fsck.

parted /dev/sdc followed by p shows

Model:  USB DISK 3.0 (scsi)
Disk /dev/sdc: 124GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags:

Number  Start   End    Size   Type     File system  Flags
 1      4129kB  124GB  124GB  primary  fat32        lba

And, finally, /var/log/user.log had:

2026-06-22T14:44:21.487543-05:00 local mtp-probe: checking bus 2, device
5: "/sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.6"
2026-06-22T14:44:21.487954-05:00 local mtp-probe: bus: 2, device: 5 was
not an MTP device
2026-06-22T14:44:21.492927-05:00 local mtp-probe: checking bus 2, device
5: "/sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.6"
2026-06-22T14:44:21.493107-05:00 local mtp-probe: bus: 2, device: 5 was
not an MTP device
2026-06-22T14:44:22.593706-05:00 local org.kde.kded.smart: Detected
locale "C" with character encoding "ANSI_X3.4-1968", which is not
UTF-8.#012Qt depends on a UTF-8 locale, and has switched to "C.UTF-8"
instead.#012If this causes problems, reconfigure your locale. See the
locale(1) manual#012for more information.

The only other logs with entries in this date range are: auth.log (me
using sudo to root), cron.log (running standard jobs) and syslog
(nothing not already seen).

Anything i need to do with locale?  Anything else I need to provide? 
Thanks for your help.