This is very much a first-world problem, but the latest versions of Minecraft (namely 1.21.3+) do not work with the mod and cause a crash. Asking ChatGPT what went wrong gives me a line of text that reads:
Caused by: org.spongepowered.asm.mixin.throwables.InvalidMixinException: @Shadow field field_20793 was not located in the target class net.minecraft.class_761. Using refmap particle-rain-refmap.json
and it tells me that "particlerain is trying to modify or reference a field (field_20793) in the Minecraft class net.minecraft.class_761 (likely LevelRenderer or similar), which does not exist in 1.21.3."

I hope this gets fixed in some way soon!

1.21.4 is now updated, but 1.21.3 is still left in the dust. Even attempting to change the .jar file to allow compatibility with 1.21.3 still causes a crash. It would be great if it was compatible with 1.21.3!

I play on 1.21.3 since a lot of mods have that as their latest version (since 1.21.4 is more of a content update than a smaller update like from 1.21 to 1.21.1)
Nonetheless, I hope you are right about the mod being updated for 1.21.3 soon.

who plays 1.21.3

it's getting updated to 1.21.3 dw