Sharing this as I found the fix, but when researching I couldn't see any posts about it, just workarounds from 2015. So maybe this helps someone in the future!
Screen flickers as I move sliders/curves etc in Photoshop on Macbook Pro 2017 (pre-M1)
In the menu, select Photoshop > Preferences > Performance and increase the Memory Usage (I used 85%, it had reset to 70% somehow)
Others had the workaround of disabling Graphics Processor, but as I noticed my Memory Usage went to 70% whereas I usually have it set to 85% I thought I would try that first. I didn't even need to restart Photoshop for the flickering to stop.