Details:
Mod File: secretrooms-1.16.5-1.1.1.jar
Failure message: Secret Rooms 6 (secretroomsmod) has failed to load correctly
java.lang.RuntimeException: Attempted to load class net/minecraft/client/entity/player/ClientPlayerEntity for invalid dist DEDICATED_SERVER
Mod Version: 1.16.5-1.1.1
Mod Issue URL: NOT PROVIDED
crash-2021-07-02_08.39.37-fml.txt

Fixed with d72fa19

I took out optifine and it still crashed with the same reason.
crash-2021-07-02_08.50.19-fml.txt