Recommended VirtualBox Version for use with Whonix ™
It is strongly advised to use the recommended VirtualBox version with Whonix ™, otherwise there can be issues. 
Instructions for installing VirtualBox on Debian Linux can be found for example on the Whonix ™ for VirtualBox with XFCE page, which contains the following text.
* Linux : please press expand on the right side.
Once expanded, the recommended instructions will explain how to install VirtualBox.
- Stable Whonix ™ Version for VirtualBox
- Whonix ™ for VirtualBox - Testers Only Version
- Install Newer Versions of VirtualBox
- VirtualBox Guest Additions and Shared Folders
- VirtualBox Troubleshooting
184.108.40.206was built and tested with VirtualBox version
6.1.26. Newer VirtualBox versions not listed on the stable version of Whonix ™ for VirtuallBox, testers-only version of Whonix ™ for VirtuallBox or otherwise in Whonix ™ News are untested by Whonix ™ developers. This can cause issues such as instability (VirtualBox VMs not starting [archive], VMs suddenly closing, host freezing, VM black screen). It is advised to wait until newer versions of VirtualBox are recommended for use with Whonix ™.
Newer VirtualBox versions are hard to install on Debian
bullseye. Perhaps the VirtualBox host software is available (even as a Debian package) from the virtualbox.org repository, but VirtualBox guest additions are not available as a Debian package. Using an older version of VirtualBox guest additions (like the pre-installed ones) might lead to broken functionality such as an inability to resize the VM or general instability. Installation of VirtualBox guest additions from ISO might also cause issues. [archive]
- VirtualBox Unavailable in Debian stable and backports due to Debian Stable Security Maintenance Issues
- Debian VirtualBox feature request: upload to Debian fasttrack [archive]
- Debian fasttrack feature request: please add VirtualBox to fasttrack [archive]
- Missing dependencies on Buster for Virtualbox 6.1.6 [archive]
- VirtualBox feature request: Guest Additions Debian Packages unavailable from Oracle Repository [archive]
- building VirtualBox from source code failing and nobody could fix it [archive], and again [archive].
checkbackport[archive] stating [archive] that creating a backport from the Debian
sidVirtualBox source package is not possible.
- Installing VirtualBox on Debian 10 / Debian buster / buster-backports / fasttrack [archive]
- Call for help:
- VirtualBox Integration
- Challenges Installing VirtualBox [archive]