The Cherno also has good videos on C++, although he assumes you have an understanding of the most common programming concepts.

Currently have 12 ISOs, 25 GB worth. Same reason, trying them out in a VM and just keep them around.

The difference from Obtanium seems to be that it presents an app-store front end, so you can browse and search for packages. Obtanium requires manual setup for each repo you want to add.

sudo apt upgrade -U -y

I think you still need to add an entry for it in fstab as well.