@pokerparties Flipping the screen 180, just makes it "upside down". Do you mean 90 degrees, similar to the difference between 'portrait' and 'landscape'?
If so, then you can just use a shader in Retroarch. That's what I do. Regardless, shaders are the way to go. (There is a "hardware" route to go with the "Pi 3" that you can't do on the "Pi 4", but I think it's CPU intensive.) You'd get better performance with shaders.