Split World (Fabric)

This is a server-side only mod that allows you to split your world in two, where on one side players will be in creative mode and on the other in survival. When you cross sides your inventory is saved and restored when you return.

Fuel the caffeine to code converter that is snaco

There is also a paper/spigot/bukkit plugin for 1.19.3 available, it is much more stable than the fabric version as of 1/12 so I would highly recommend using this with a paper server to get the best results.

Paper / Spigot / Bukkit Plugin