Never mind. I think I solved it. It was one of two things (or both): 1) There was a PPI mismatch between the photoshop template and my art assets. Not sure why that should matter when they both come out to the same pixel count. But maybe... 2) My first attempt I left out the lowest resolution icon assets in Xcode. I just wanted to make sure the full size icon looked okay before moving on to the less detailed lower resolution variations. But maybe leaving out the smallest file broke something. Whatever the case, my photoshop template is working fine and my icon is now proportionately correct.

I'm glad it's not just me. Was beginning to think there was something wrong with my Mac. I bought the i9 iMac and really spec'd it out; built to order. But on Big Sur I get stutter animations. If I slowly move my mouse around the cursor is jittery. Almost like it's a bluetooth error but I know it's not. Watching videos and some of them will stutter too. Scrolling stutters. I have to shutdown my computer and restart to clear it up. And my Apple Wireless Keyboard is not wireless anymore. I have it plugged directly in with a lightning cable because trying to type on it wirelessly would lag and mess up. This is pretty ridiculous. I hope macOS 12 fixes this.

I’ve not found a solution either. Since I switched to the Xcode 13 RC, all of my beta testers are now crashing! This is holding up a release.