I’m not sure that it is Cinnamon, but Cinnamon does let you put things in the middle of a panel, so it’s pretty easy to make something similar to that.

If the installation set up updates using apt, even if it uses a separate repository server, then Update Manager should still update them. I have personally seen updates from third-party sources show up in Update Manager. For example, I’ve installed Proton VPN using these instructions and it does receive updates using Software Manager.

If you installed Mullvad using the “Ubuntu/Debian” instructions here, then I think it should get updates through Software Manager, but I haven’t tried this browser myself.

For any other software, it depends on how it’s distributed.

Is this even true? I am fairly sure that Linux also has a graceful shutdown process, but I’ll admit I haven’t looked into it.

I think it’s funny for the exact same reason that this xkcd is funny: https://xkcd.com/1168/