Yes, I have 'reduce transparency' set to true. Overnight after upgrade the UI became noticably sluggish.
The outstanding example is Spotlight. For years since the M1 release I have been able to bring the bar up and type C-H-R then Enter, in ~500ms I guess, and I would always get Chrome.
Now, I have to wait another 1-2 seconds for it to think. If I hit enter before it has finished thinking, Spotlight goes away and nothing else happens!
The UI and Spotlight are still fine on my 2020 M1 Air running Sequioa