I've tried v 2.2.0 and v 2.0.0 for both my client and server and I get this issue even for the official server, my friend who I asked to try it also has the same issue on my server and the official, any idea how I would go about sorting this? I've reinstalled the pack for both versions and nothing changed.

This is not an issue with the modpack, you should be able to join the server anyways, Forge only says that because the server doesn't have client-sided mods.

Both me and my friend are unable to join as it immediately disconnects us from both my server and the official one.

The official server is still on version 1.16.4-1.0.1