Stupid question about upgrading VirtualBox

[fth0]

Quite, my apologies, what I should have said was that a search in the VMbox *included* documentation

Then I don't understand where you're looking:

The documentation included in VirtualBox 5.2.44, 6.0.24, 6.1.42 and 7.0.6 all contain the chapter that I linked to in the online documentation, and it hasn't changed in the last 3 years at least. I deliberately left out the chapter number, because there is also a different online documentation at Oracle with different chapter numbers.

Ah, I just noticed that "12.7.5" indicates that you must be talking about some other documentation ...

[arQon]

My description wasn't accurate: On my Linux Mint 20 host (based on Ubuntu 20.04), a double click starts a program named gdebi, which is a GUI app for .deb install files. So I possibly wrongly assumed that on Ubuntu 20.04 the same would happen.

gdebi is in "universe" in Debian: it's unlikely to be around in a default install of any derivative, I'd expect (and rightly so, as it's desktop-dependent) - certainly a small minority at most.