When joining a server like Hypixel, the client immediately crashes

Logs: https://mclo.gs/K0dDakT

Minecraft 1.21.4, fabric loader 0.16.14
Mods used: Wavey Capes 1.5.2, fabric api 0.119.2

You installed the 1.21(.1) jar in 1.21.4. Use the 1.21.4 jar.
(Seems to be some Prism Launcher issue, had a few people now with different mods, installing the wrong version on Prism)

Oh ok, maybe it is more like a Modrinth tagging issue, because prism launcher downloads from there and here it is written that the version for fabric 1.21.4 is Wavey Capes 1.5.2:

Which one is the correct jar, then ?

1.5.2 is the mod version, thats the same for 1.16.5 - 1.21.5. You need to make sure it's the correct mc version/modloader.

And as I said, it's probably a Prism issue. It downloaded https://modrinth.com/mod/wavey-capes/version/oyiyHkeB instead of https://modrinth.com/mod/wavey-capes/version/xWqFqiiF