I have prepared this update to VirtualBox 6.1.20.
It build in poudriere with default options and runs on my system for light loads.
I plan to commit this once I'm done testing, I'm posting it here so others can take a look too.
This patch does not include the changes I sent in bugzilla bug 255208 trying to fix the additions vboxvfs module kernel panic inside jails.
I plan to commit that before proceeding with the update.