Minecraft Version: 1.21

Forge Version: 51.0.23

Mod Version: 1.20.1-0.0.14.jar

Single Player or Server: Server

Describe problem (what you were doing; what happened; what should have happened):
Installed Forge Server, Flib, and Creeperheal.
When trying to start the server, server fails to start due to missing class IConditionSerializer.
Removing FLlib and Creeperheal resolves issue and server starts normally.

Log file link:
https://pastebin.com/Qm2CHmve

oh dang I'm dumb and just realized that you don't support 1.21, you support 1.20.1. Thats what I get for putting in bug reports at 1am. Sorry about that.

Hope you update soon though I'd love to run creeperheal