Appimage is terrible. It works by trying to make applications in appimages adhere to a lowest common denominator between Linux distros... which amounts to forcing application developers to develop for the oldest version of Linux appimage supports.

Nix is a huge pain to deal with.

Nix makes me think of the old Zawinski joke of:

"Some people, when confronted with a problem, think 'I know, I'll use regular expressions.' Now they have two problems,"

Except there are less upsides for using Nix over something like OCI.