I succesfully installed Devuan:

devuan_beowulf_3.0.0_amd64 guest
on VirtualBox 6.0.20-137117
on Windows 10 host

This replaces Debian:

Debian 10.1.0-amd64-xfce-CD-1 guest
on VirtualBox 6.0.22-137980
on Windows 10 host

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I have no complaints with my installation, including nuances available
only through the VirtualBox "Guest Additions" (shared folders,
copy-paste, dual screens).

One minor issue is that it does not resize into my full desktop
resolution when I fullscreen, but I don't care.

Fine work guys!

I had an intermittent audio hiccup issue under Debian 10.1.0-amd64
which I have yet to reproduce under Devuan.

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Note that I had persistent issues using other versions of VirtualBox
which were solved with the specific version/build "6.0.20-137117":

https://download.virtualbox.org/virtualbox/6.0.20/

e.g. for Windows host:

https://download.virtualbox.org/virtualbox/6.0.20/VirtualBox-6.0.20-137117-Win.exe
https://download.virtualbox.org/virtualbox/6.0.20/Oracle_VM_VirtualBox_Extension_Pack-6.0.20-137117.vbox-extpack
https://download.virtualbox.org/virtualbox/6.0.20/VBoxGuestAdditions_6.0.20.iso

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Notes and troubleshooting:

https://blog.spiralofhope.com/?p=6969#2020-06-05_6.0.20-137117_Devuan-beowulf_3.0.0_amd64
https://blog.spiralofhope.com/?p=5856#2020-06-05_devuan_beowulf_3.0.0_amd64