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://www.curseforge.com/minecraft/mc-mods/irisshaders/files/all?page=1&pageSize=20&version=1.20.4&gameVersionTypeId=4

Minecraft version

1.20.4

Describe the issue

The mod requires the minimum version of Iris 1.6.17
but I have the version of Iris 1.7.0+mc1.20.4!

Probably fixed in 5.1.8