For personal files/media, I heard about the 3-2-1 method: 3 copies, 2 formats, 1 offsite. I'd likely want to add a complete self-contained toolchain to convert format with that offsite copy.

I'm not nearly as particular with my OS backups as I used to be. For instance Desktop personalization is minimal. I've used too many computers over the years to maintain much configuration beyond a small number of dot-files. Hobby code goes in Github/codeberg.org and some kind of cloud sync for my daily driver.

Another thing that ended up happening naturally is that I keep hard drives of old computers when I upgrade. They serve as point-in-time snapshots. I haven't made it a point to be able to necessarily read all of them but it doesn't take much like having a number of USB-disk/media interface adapters around.