Minecraft version: 1.21.4
Modloader: Fabric
Fabric loader version: 0.16.10
Environment: Singleplayer / Multiplayer

Mod name: Ore harvester
Mod version: 1.21.4-1.4

The Mod doesn't work on Minecraft Realms or Multiplayer, only in singleplayer, the dependencies are installed, i have the tree harvester installed too and it doesn't work either on Realms, only in singleplayer, sorry for my poor english.

The mod needs to be installed server-side, which Realms don't support. That's why it does work in singleplayer, which simulates a server. You can try to self-host a Fabric server. Thanks for giving them a try!