When installing fabrication version 3.5.6-1.21 onto minecraft 1.21.4 with fabric version 1.16.10, the game crashes immediately, complaining of a mixin mismatch:
https://gist.github.com/torzod/97acafdb7f453579f1fe7bad45c5ff18

fabrication is supported on 1.16 - 1.21.1

ah, ok thank you! the version file was titled 1.21, which is ambiguous as to its highest supported version