So does anyone have a good strategy for transferring non giant things? Like I have a ton of unorganized pictures, documents, videos dating back to my 2009 1TB HDD that still works.
I think I want to run Debian mostly because I don't know any other build well. Well RHEL, but I want to keep it similar to the Steam Deck as I can
Dump it into a NAS. Synology makes a decent 2-drive NAS that is easy to maintain. They have a decently long lifecycle and even upgrading hardware is usually just moving the drives to the new unit and powering it on.
1TB is easy, a sata to usb 3.0 adapter is like $10 and will transfer all that data in a few hours. If you are more patient just setup the drive as shared in windows and transfer it over the network. I just copied about 7TB a few weeks ago to a new NAS over the network and I had it done over the weekend.
If you want to play games, then Debian isn't that good of a choice because of the outdated packages. I'd suggest getting a new SSD though. Your HDD is already pretty old and slow and could potentially fail soon, so you might as well get some fresh storage. Makes it easy to test distros too until you found something satisfactory, at which point you can transfer over your old data and eventually format your old HDD into some sort of backup drive I guess.