It seems that VirtualBox is not (and will not be) available in Debian-10-Buster backports ( as per Debian wiki ) so the instructions on the Whonix wiki don’t work. Are there any downsides to using the repository at [download.virtualbox.org] instead as per [tecadmin.net/install-virtualbox-on-debian-10-buster/] ?
Documentation was updated just now. The part which answers your question is quoted below at the time of writing but users should read if from the up to date version going to and going from there:
It is quoted here for convenience, for easier quoting from it and discussion.
These instructions are for Debian buster , which is recommended. Other Debian releases might work, but this is untested. In that case, replace buster with the actual codename your release.
Note: this applies to Whonix 15 . Later Whonix versions may use a codename different to buster .
Package virtualbox should be installed from Debian unstable (codename: sid ). This is non-ideal but required since VirtualBox in unavailable in Debian buster / buster-backports at the time of writing. It has risks such as bricking the apt package manager. Therefore users should make sure to have their backup and restore process functional. Alternativly you could install from Oracle Repository but this comes with different risks.
Virtualbox is not available in Debian 10 (nor in backports). The reasons are discussed at length in https://bugs.debian.org/794466 and various other mailing list threads, but can be summarized as:
Virtualbox is not suitable for Debian stable releases because of the lack of cooperation of Oracle on security support (that’s the Debian security team decision).
Since it is not suitable for stable releases, it cannot be included in the testing suite (that’s the Debian release team decision).
It also cannot be included in official backports, as packages must be in testing before they get backported (that’s the Debian backports team’s decision).
Whonix ™ 15.0.1.3.4 was built and tested with VirtualBox version 6.1.6 . Newer VirtualBox are untested by Whonix ™ developers and can cause issues such as instability (VirtualBox suddenly closing, host freezing, black screen).
Newer VirtualBox versions are hard to install on Debian buster . Perhaps the VirtualBox host software is available (even as a Debian package) but VirtualBox guest additions are not available as a Debian package. Using an older version of VirtualBox guest additions (such as the pre-installed ones) might lead to broken functionality such as inability to resize the VM or instability. Installation of VirtualBox guest additions from ISO might also cause issues.[archive]
Therefore we are stuck with VirtualBox version 6.1.6 .