Well I guess I didn't really break it. A KDE update broke it. After updating I rebooted, and then when I tried to log in, the screen went black and got stuck like that.
Anyway, I read on the forums that the fixed involved adding a parameter to some line in the kernel options, which I had no clue how to do. I also didn't know I could enter the terminal from a frozen screen. So I tried the grub menu. But I didn't know what I was doing and was scared to mess things up, and for some reason I thought the answer was in the UEFI screen.
Now I knew that I was treading in dangerous waters, so I was trying not to touch anything while poking around the menus trying to figure out where I needed to go. But apparently I touched something I wasn't supposed to, cause my computer tried booting from the spare SSD, which isn't mounted yet and don't know how to decrypt it. So I got stuck for a while, tried the grub rescue in the command line because it was the only option I seemed to have, didn't understand it, panicked for a while, and eventually found out I could press f2 on startup to go straight to the UEFI screen. So then I went back to the menu where I messed things up and made sure to click on the correct disk.
So I was quite relieved when I was able to decrypt it and it brought me back to the Endeavour grub menu (the purple screen), and then booted up as it was supposed to. I tried logging in again and it still froze, but at this point I had learned I could press some hotkeys to get to the terminal. So I went in there and followed some instructions I found, ultimately only really learning what the problem wasn't. It turns out the parameter I was supposed to add to fix the issue was already there!
So I found out how to revert kde desktop and workspace to a previous version from the cache, and I did that, but when I rebooted and tried logging in again it still froze.
Luckily I had previously made a guest account so I logged in there and it worked. So then I learned that that means the issue was in the user-level configurations.
So I followed some more instructions to back up my KDE configs, moved the existing ones to somewhere else, then killed and restarted plasmashell to create new default config files.
And then I tried logging in, and it worked! This was an hours-long process, so it definitely felt good to have a working system again.
Luckily most of my settings and my favorited items in the app launcher were still intact. I hadn't moved my global shortcuts config file either, so my keybindings were preserved. The only things missing were my pinned icons on the app manager toolbar at the bottom of the screen.
So I went into my backup file for the plasma appletsrc configs, and I found the line that listed the apps I had pinned, and I copied it and used nano to paste into the current version in same place it would have been.
So even though it was tragic and frustrating and a bit gut-wrenching at times, I learned a LOT today. I gained some familiarity with grub, UEFI, terminal, basic shell commands, restoring previous versions of software from the cache, logging and troubleshooting, backups, configurations, and the basic system architectures, and the anatomy of the KDE environment.
I'm still no power user, and I still have a lot to learn, but I came a long way in just one day. Now, I'm tired.
There's lots more to set up tomorrow, but at least walking into it I won't feel so lost!
This noob rocked It though! They went from zero to hero using only willpower and a search engine.
Hahaha, thanks!
~Psst, here's an embarrassing secret:~
~I ended up using Lumo to walk me through the steps after despairing when my system wouldn't boot. I had been using the forums but they seemed to assume a certain baseline level of knowledge, like "go here and paste this," but I didn't even know how to get to a terminal with a frozen desktop, or what commands to run to get to the place where I needed to paste stuff. Things like that.~~Lumo explained every step, and even though it was a bit confused at first (at first it wanted me to physically remove my SSD and reset it, then wipe everything and reinstall!), I was able to talk it down from the ledge until it finally just told me "Oh yeah, you can press f2 at startup to get back to UEFI without decrypting." Like, thanks... I guess...~
~And then when I got back into my system and was in the terminal, I looked up all the commands it told me to run before running them so I knew what they would do. Things like nano, journalctl, lsblk, tar, mkdir, etc. I already knew what sudo and pacman do.~
~But overall, my problem was too specific and the solutions I had found in the forums, even if I understood them, ended up not applying because the parameter I was supposed to paste somewhere in the kernel options ended up already being there when I finally figured out how to get there. And I just didn't have the level of basic knowledge it would've taken to simply follow the advice in the forums without expanding a whole rabbit hole skills tree of basic tutorials, all while panicking and thinking most of it looked like gibberish anyway.~
~So I don't regret my decision, because ultimately it worked. I get the dangers of using AI and vibe-coding, but I double-checked everything before running because I'm not an idiot. Also, Lumo generally seems better at programming than other LLMs. Probably because it isn't designed by a greedy and corrupt, power-hungry and profit-driven american corporation, so it avoids enshittification. I'm not evangelizing, just relating my experience.~