Linux 101 stuff. Questions are encouraged, noobs are welcome!

I've just put Fedora40 on my Lenovo legion. I installed kde spin. I've got two strange issues.

The first, when adding file attachments in Firefox, it opens the gnome file manager instead of dolphin. Annoying but not major.

The second, when playing a steam game (fallout4) on multiple monitors, it seems the mouse isn't trapped to the game window, and when it inevitably makes it's way to the second monitor, a click will change focus. For this issue, I have been trying to use the kde window rules, but that doesn't seem to work. Nine of the rules seem to force the mouse to stay in that window.