This would happen on the debian side of things

Thanks for the answer @g0tmi1k.

Since it is imported on unstable on Debian side and it seems that it is not automatically imported in kali-rolling (4 versions are missing see https://tracker.debian.org/pkg/virtualbox), maybe it needs to be manually imported ?

It does need to be manually imported, as we are based on Debian testing ~ https://www.kali.org/docs/policy/kali-linux-relationship-with-debian/
& https://www.kali.org/docs/general-use/kali-branches/

As its such a key part, it may be worth waiting for it to go from Debian unstable to testing to help reduce the chance of bugs

Yes you are right, but it will not make it to testing or stable:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=794466
https://tracker.debian.org/news/1038163/virtualbox-removed-from-testing/

VirtualBox is an exception and needs to be imported from unstable (automatically ?).

In the future (kernel update), VirtualBox kernel modules will breaks and the package will be unusable if not updated.

virtualbox version 6.1.22-dfsg-2 has been imported in kali-rolling.

The version 6.1.22-dfsg-3 will not be imported for the moment in kali-rolling because of a build failure in Debian.

But i was talking about upgrading to version 6.1.26 not 6.1.22.

the version 6.1.26 has been uploaded in Debian.
I just imported the package version 6.1.26-dfsg-4. It will be available very soon in kali-rolling