I wanted to play Pehkui mod on 1.16.5 with immersive portals but as soon as i walk through a portal (two diffrent sized portals so i should shrink/grow right?) the came crashes and gives me this crash log:

The game crashed whilst unexpected error
Error: java.lang.NoClassDefFoundError: net/minecraft/command/arguments/IArgumentSerializer
Exit-Code: -1

I play on fabric-loader-1.16.5 with these mods (with file name idk if this is useful for helping):
-Pehkui (Pehkui-2.0.0+1.16.5-forge.jar)
-Immersive portals (immersive-portals-0.90-mc1.16.5-fabric.jar)
-fabric (fabric-api-0.32.9+1.16.jar)

I don't really know what to do about it ._.

It works now, thank you for helping me (even if it was just a fault by me and not an issue, sorry for that btw) and your time.

No problem. Glad to be of assistance.

You appear to be using the Forge version of Pehkui on Fabric. Can you try again with the Fabric version?

You mean that one? "Pehkui-2.0.0+21w14a.jar"

Yep.