What's wrong with my debug screen?

Solution 1:

The server has the gamerule reducedDebugInfo true set.

This is a setting to give less gameplay-related information in the debug screen. It hides your coordinates, your block coordinates, your facing direction, the biome you're in, the light levels, the local difficulty and the coordinates of the block you're looking at, as well as the lines of F3+B (hitboxes) and F3+G (chunk grid).

The reason it's set on some servers is to prevent players from using the debug screen in their regular Survival play, because it's originally intended only for debug purposes and some people consider it cheating to use it in Survival.

There usually is no reason to set it on a Creative server with access to commands. If the server owner allows it, you can change it with /gamerule reducedDebugInfo false.

Solution 2:

According to a Reddit thread, you can solve this through Options>Multiplayer Settings>Reduced Debug Info: Off.