Is it a mod compatibility issue?

Yes

If it's a mod compatibility issue, please provide the link(s) to the incompatible mod(s)

https://modrinth.com/mod/iris

Minecraft version

1.20.1

Describe the issue

iris updated in the recently and the version check needs updating. should probably also be a warning, not a strict compatability check, so minor version updated dont prevent loading the game and the user is left to decide if there is an issue or not

This mod lock Iris version because this mod uses Iris internal that may break in new versions of Iris (this happened many times at past).

For now, you can use dependency override https://fabricmc.net/wiki/tutorial:dependency_overrides to get rid of the restriction (but it may crash in-game)

Put fabric_loader_dependencies.json into config folder with these content:

{
    "version": 1,
    "overrides": {
      "immersive_portals": {
        "-breaks": {
          "iris": "IGNORED",
          "sodium": "IGNORED"
        }
      }
    }
  }

Probably fixed in 3.3.7