The problem is that you're trying to do shit like if you were still on windows. Linux doesn't really have startup applications, we use daemons for everything that needs to start with the OS, everything else is meant to be launched manually.
However you can still do what you're asking for, and it'll depend on the DE not the distribution. Ubuntu and Pop OS use gnome that has an option to set startup programs in gnome tweaks.
Blizzard games have always had good linux compatibility. Might change now that they've bought by microsoft though.As for ubisoft games they probably run too, launchers are a pita but they do run, you'll need something like lutris, bottles or heroic launcher to get you started running shit outside of steam, they're not necessary but they make things simpler.