And don't skip over reading things! I also run Arch with KDE and honestly with almost all problems I have, if I carefully read through either the Arch Wiki (this will probably be your most valuable tool) or the error message that comes up, the answer is usually in there somewhere, it just needs digging up.
Also: if something with a GUI crashes and doesn't give an error message, try running it in the terminal. So like, if Firefox crashes and doesn't give any info, try opening up a terminal and running firefox from there and the terminal will tell you everything that's going on. (It'll be a different command if you're using a flatpak but that's the general idea.)