I've been using NixOS for nearly a decade. It took me several days to understand the filesystem layout, and I had the advantage of knowing some capability theory beforehand. However, once I understood the Nix store, my paradigm shifted and I haven't had any further "unexpected troubles."
As far as I can tell, AppImages and Flatpaks are extraneous, heavy, improperly isolated, and propagate a sprawling filesystem which is hard to secure. Compare and contrast with Impermanent NixOS, which only persists data that the user has explicitly marked to be saved and has systemwide caching of installed applications.
I'm the only one talking to you. You've convinced nobody else that you're even worth speaking to. Honestly, you sound like the weenie who tried to publish that bootlicking pro-military letter. Wanna go be the second person to sign it? You certainly aren't doing anything worthwhile with your time here on Lemmy.