Windows hides file extensions by default. When you renamed the file, you accidentally changed the extension.
Refers to . As of mid-2025, 1.21 (the Tricky Trials update) introduced new blocks, trial chambers, and the mace weapon. Meteor Client updates frequently to support new versions. The 121 ensures the mod is compiled against the correct mappings and network protocol. Using a 1.21 mod on 1.20.4 or 1.21.1 will crash the game or fail to load. file name meteorclientmodfabric121jar new