GPU Acceleration is enabled, but I still get the error message Premiere pro 2020

This issue has only sprung up recently. In my project settings I select the "Mercury playback engine GPU acceleration (Metal) - Recommended" and yet I still get the "This Effect Requires GPU Acceleration" error message over my clips using certain effects. I am on a 2020 iMac running macOS Big Sur version 11.2.3 with a 3.3 GHz 6-Core Intel Core i5. I'm not sure what the problem is.