This isn’t a part of macOS 26 that bothers me, honestly. I don’t spend a lot of time stacking windows and measuring their corners.
I can compare Safari to System Settings and they have the same new rounding. It's nothing to do with utility vs "main" (whatever that is)
(Search for "radius" in the transcript.)
There are things which definitely do bother me like the Liquid Glass, but the window corners really don't bother me. And I'm into design and constantly inspect parts of ui with Digital Color Meter app.
I used to roll my eyes at the complaints until I actually had one of these, and it is appallingly bad engineering. Especially since the previous design, which was functionally identical just needed a 10 second battery swap.