When using shaders using Iris, the buttons that are supposed to appear on the screen actually appear as an overlay in the bottom left corner of the screen.

Expected Behaviour: Buttons are shown on screen block
Actual Behaviour: Buttons are show on the bottom left corner of screen in absolute space

Sorry for taking too long to answer but this is already known. I already talked to the Iris devs and they said they'll be looking for a way for mod devs to fix incompatibilities like that in the future.