The problem with newer versions of Linux Kernel 5.10 such as Liquorix Linux Kernel 5.10-12 and the VirtualBox package from Debian Unstable has been fixed.
The new virtualbox 6.1.18-dfsg-1 package has addressed this issue:
virtualbox (6.1.18-dfsg-1) unstable; urgency=medium
[ Andrea Righi ]
* debian/patches/linux-5.10-TASK_SIZE_MAX-replaces-USER_DS.patch:
- upstream patch to fix build failure of virtualbox-guest-dkms with linux
5.10 (LP: #1908734)
* debian/patches/linux-5.10-drm-fixes.patch:
- upstream patch to fix multiple virtualbox-guest-dkms drm's build
failures with linux 5.10 (LP: #1908734)
[ Gianfranco Costamagna ]
* New upstream version 6.1.18-dfsg
* Drop kernel 5.10 build fixes, upstream
* Refresh patches
