Before Continuing:

• Always check you are using the latest version of the mods and its dependencies
• Remove known problematic rendering mods such as Optifine, Sodium and others. Do NOT report issues related to said mods
• If you are unsure which mod is the culprit.
  Disable half your mods at time until you isolate the culprit
• If you have a crash ALWAYS post LATEST.LOG below
• If the issue is about behaviors be sure to consult the WIKI first

Version-Loader

1.20.1-forge

Supplementaries Version

supplementaries-1.20-2.7.22

Moonlight Lib Version

moonlight-1.20-2.8.81-forge

Issue Detail

When I use Velocity to proxy Mohist and give the player op permission, he will be kicked out of the game!

wlm123 lost connection: Internal Exception: io.netty.handler.codec.EncoderException: java.lang.IllegalStateException: Registry moonlight:map_markers not found

Optional Attachment

wlm123 lost connection: Internal Exception: io.netty.handler.codec.EncoderException: java.lang.IllegalStateException: Registry moonlight:map_markers not found

To Produce

When I use Velocity to proxy Mohist and give the player op permission, he will be kicked out of the game!

Velocity is for Vanilla!!!!

This is their issue. If they are nuking mod-added datapack registries they are not incompatible with a mod, they are incompatible with forge architecture and modded in general.
Dont use said hybrid servers for modded, its a known fact that those people make thsoe for vanilla and dont care if stuff doesnt work for mods