I find the greatest challenge with giving Linux to others, is what story to tell: You're running Mint. That's a Linux distro. It's based on a different distro called Ubuntu, which again is based on Debian. Your desktop, though, is called Cinnamon. So when you have a problem, you must search for a solution in that order: Cinnamon, Mint, Ubuntu, Debian.
When installing packages, you have native packages, through apt-get,
but you also have flatpak, snaps and appimage. Graphical frontend?
Sure, you've got (at least) 2 different ones installed. When to use
which? Try them out and see which one you like the best. If they don't
work, try synaptic, it's not pretty, but that always works. Oh, but
it doesn't work with flatpak or snaps, so you need to be aware of
that.
Good luck 😁
