alt Hacker NewsZstd for example only promises determinism on the same version of the library. I've personally seen the hashes mutate between pull and export. Things like tar padding also make a difference. Really, the thing to do is to hash on the _uncompressed_ data and let compression be a transport/registry detail. That's what I've done, at least.
I didn't know that about zstd, that's a bit unfortunate.
Tar isn't related here though, we're talking about compression not archival formats