What about that interminable animation every time you fullscreen a window or switch between fullscreen windows? It should be at least twice as fast and there's not even any way to hack it to speed it up. You just have to live with it. ("reduce motion" changes it to a crossfade but doesn't make it faster)
While we're at it, the Dock has always been bad. And the top menu bar was good for the original Macintosh with a tiny screen but it makes no sense on a 4k display with many different app windows showing simultaneously. MacOS has a lot of relics of the past that Apple refuses to give up. I just see it as a tax I have to pay to get to use Apple Silicon.
Maybe it's inherently slow, because it's a "loading transition" like in video games. Takes a second for the new backing virtual desktop to be allocated, and for the window to potentially grab new assets to redraw (think: resizing iMovie window larger ⇒ larger timeline preview ⇒ re-rendering timeline thumbnails); and the animation plays on the old desktop while this is going on in the background on the new desktop, so that when the animation completes, the new desktop is "ready" for an atomic single-frame cut-over, rather than ugly pop-in happening and the app still being blocked on input.
Probably also has some constraints imposed upon it due to requiring that virtual desktops transition smoothly over Screen Sharing, where texture assets are being sent and buffered to a remote compositor.