Going to try my best here, but tbh I was going to use Ubuntu because it was supposed to just work out of the box and I don't know much about any of this :(
Background info: I'd been running Ubuntu 20.04 with increasing weird errors on my Thinkpad P50, so I thought I'd do a reinstall to 22.04. I was having weird issues with the USB startup disk too, so I had someone create one on their Windows laptop. Got a 452 out of range pointer error, but it ran after switching to UEFI in the Bios (it was set to Legacy only but I have no idea what this means). Got through the installation process and was prompted to restart. No dual boot or anything special that I'm aware of btw.
Current issue: When trying to boot my freshly installed 22.04 (ETA on my Thinkpad P50), I get two outcomes depending on Bios settings. With UEFI I get a boot loop, sometimes "Reset system" shows up for a second. With Legacy I get "error: file '/grub/i386-pc/normal.mod' not found" and a grub rescue prompt.
I've tried to reinstall from USB, same result. I can boot into the "Try Ubuntu" environment.
UPDATE: I managed to find out about boot-repair and it was supposedly repaired, but nothing changed. I got the URL
https://paste.ubuntu.com/p/GvjKHvz8Vw/
It also says to make my UEFI firmware boot on some Ubuntu entry with a path to a grubx64.efi file, which I've tried to look up with no clear answers.
UPDATE 2: Seems like Will was correct and at least part of the problem was the installation media, as I managed to install and boot a slimmer distro from an old USB stick (though with limited functionality, see comment below).
My friend found another large enough USB stick to experiment with. I found discussions on the P50 not meshing too well with Ubuntu, but good experiences with Mint so I might try that one (even though it is based on Ubuntu?).
(Where do I go from here? I can't even go back to Windows as my device was second-hand. I'm willing to try a different Linux distro if it's not too complicated, I really just want anything that works without much trouble :( )
Thanks for any advice.
UPDATE 3: I installed Mint from a different USB drive, and it didn't boot either. UEFI leads to boot loop as with Ubuntu, Legacy to a Boot Menu where nothing happens and an App Menu where I ran all the diagnostics with nothing found.
I'm having attention deficit issues, but I'm trying to get through the system-info script and am going to look into BIOS updates as recommended below (thank you).
Hopefully last update. I finally managed to get into the grub menu (after failing earlier) and added nomodeset for my last install, which was Mint. It seems to work so far, so I guess I'm a Mint user now because I'm not going to risk screwing things up again. This may or may not have worked with Ubuntu (as I said, I chose the option to install proprietary drivers right away; Mint didn't have that option). I should probably still find a way to update my BIOS, but that's going to be a post for some other time, maybe.
I'd like to thank everyone in this thread for your patience with me.