Whether you are on 1.21.3 or 1.16.5, these are the "must-have" modules for survival:
Meteor Client remains the gold standard for modern utility mods. Its jump to the 1.20.x and 1.21.x snapshots has been handled with surprising stability, retaining the aggressive, fast-paced playstyle that made it famous in the 1.16.5 era. Meteor Client 1.21.3- 1.20.6 -- 1.16.5