Help I'm getting an error when I try to startup my server

I'm using a server so not a "development environment" meaning I can't ignore it?
Everything still works fine but I don't really know what to do

Server:

• Minecraft: 1.16.5
• Forge: 36.2.22
• Host: my own pc
• Memory: 2048MB
• Player limit: 10
• Total mods installed: 13

Mod:

• Version: 0.4.2-1.16.5

It's just a warning, I'll see if I can fix it in the next update.