Community for all things Commodore Amiga related.
This is anekdotal and just describes my personal experience in the 90s:
I can't remember quite when I did it, but I upgraded my A500 to KS2.0 back when it was the latest release of the OS somewhere in the 90s. I never found a huge problem with compatibility for games or anything else.
My memory expansion still needed to be disabled for one or two games (by means of a little switch on the side of the case), but for the most part everything seemed to just work.
I'm not sure about compatibility lists but from what I understand, it's only a handful of early and badly behaved software that requires 1.3. It's probably better to just install 3.1 and use Relokick as needed to run incompatible software.
Does 3.1 have elevated system requirements?
I'm not actually sure what the minimum requirements are for 3.1, except I know that 3.1 upgrades were sold for the A500/A2000 so it should work on a classic configuration. I know that the newer Hyperion updates to AmigaOS raise the requirements quite a lot, so I wouldn't try going to 3.1.4+ without an accelerator/fastram.
@SanguineBrah @edgerunneralexis ISTR 3.1 was a bit more intensive than 3.0 according to Amiga mags I read. I think 3.0/1 might need 1mb chip min whereas 2.0 can run in less.