Is it a mod compatibility issue?

Yes

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

add compatibility to iris 1.6.10+1.20.1 to immersivePortals and portal guns in 1.20.1
https://modrinth.com/mod/iris/version/DsjYuGMO
https://modrinth.com/mod/iris/version/DsjYuGMO
https://modrinth.com/mod/iris/version/DsjYuGMO
https://modrinth.com/mod/iris/version/DsjYuGMO
https://modrinth.com/mod/iris/version/DsjYuGMO

Minecraft version

1.20.1

Describe the issue

add compatibility to iris 1.6.10+1.20.1 to immersivePortals and portal guns in 1.20.1

Same issue, not compatible.
Edit: Nevermind the new alpha version 3.3.4 works. Curseforge said all mods were up to date while it actually wasnt. TY.