I am working on a 1.18 pack and found the Mining & Caving Portals don't work. I then tried it in a fresh install with no other mods, except the Mining Dimensions and it still did not work.

Minecraft Version: 21w43a snapshot 1.18
Mining Dimensions Fabric: 1.18-21w43a-1.2.19
Fabric: 0.12.3

Mentioned on webpage:

Mining portal changed to deepslate, caving dim changed to tuff

Thanks, that works great!