Minecraft datapack that 'pauses' the worlds when no players are online. This useful for keeping the local difficulty the same when no players are online.
The datapack files can be downloaded from here
Extract the zip when downloaded. Then put the PauseWhenEmpty folder into the datapacks folder of your world save. This will activate PauseWhenEmpty automatically on the next server startup.
In the case your server is already running, just run the /minecraft:reload command and it should start. (Note: on a unmodified Minecraft server the command for this is /reload)
For a clean removal use the /function pwe:remove command first. After that you can remove the datapack files out of your datapacks folder.