I fixed it and it was again the same problem from the last post!
Delete the "World" folder and open the Forge-1.16.4-35.1.37.jar file to create the Modded world.
Do Not click the Minecraft_server.1.16.4.jar
Clicking that will create a vanilla server.
If you did make sure to delete the world folder and click the forge one instead.
Hope this helps anyone with this problem
So I'm making a Forge server with mods for my friends (as you do) and when I attempt to log into the server it give me this message "Internal Exception: java.lang.ClassCastException: net.minecraft.world.biome.Biome$Category cannot be cast to java.lang.String" I'm doing it on the Forge Desktop app so idk how to get the crash log to know what mods don't like each other and which biome is making it's little self a string so i'm at a loss. I looked up this same error but the person was able to provide a crash log due to it being on the Twitch app. Well that updated and its now moved to the Forge App.... Help?
List of Mods:
Structurize
Alex's Mobs
Biomes O' Plenty
Citadel
Druidcraft
MineColonies
Structure Gel API
Valhelsia Structures
Wyrmroost