I've created a partition devuan-root in a volume group before this.

I then create an ext4 file system in that partition

But I cannot mount it.

april:~# mke2fs -n -t ext4 -j -L devuan-root /dev/VG-3T/devuan-root
mke2fs 1.44.5 (15-Dec-2018)
Creating filesystem with 15728640 4k blocks and 3932160 inodes
Filesystem UUID: beec99ef-ab48-4460-b19c-d0f6cc43aa33
Superblock backups stored on blocks: 
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
        4096000, 7962624, 11239424

april:~# mount /dev/VG-3T/devuan-root /newroot
mount: /newroot: wrong fs type, bad option, bad superblock on /dev/mapper/VG--3T-devuan--root, missing codepage or helper program, or other error.
april:~# ls -al /newroot
total 8
drwxr-xr-x 2 root root 4096 May 16 18:59 .
drwxr-xr-x 63 root root 4096 May 16 18:59 ..
april:~#

It does not help to specify ext4:

april:~# mount -t ext4 /dev/VG-3T/devuan-root /newroot
mount: /newroot: wrong fs type, bad option, bad superblock on /dev/mapper/VG--3T-devuan--root, missing codepage or helper program, or other error.

And my system can hande ext4:

pril:~# mount | grep farhome
/dev/mapper/VG--3T-farhome--3T on /farhome type ext4 (rw,relatime,quota,usrquota)
april:~#

I have no problem accessing stuff in /farhome:

april:~# ls /farhome
 alice         hendrik      lovehome                  parents                 upgrade-lenny2.time
 aquota.user   home2        lovesong-20072002-df-Tl   seraviel                upgrade-lenny.script
 geoffrey      kira         mke2fslog                 shadowstuff             upgrade-lenny.time
 gwen          lost+found   oldtopoi                  upgrade-lenny2.script  'usr=src=modules=nvidia-kernel'
april:~#

-- hendrik