Except it kind of fails at that too. The window corners seem to be either based on those squircle things or some kind of other varying radii curve which eases out into sides much more gradually than proper circles. The window buttons (close, minimize) the round toolbar buttons anchored to top right corner are based on proper circles. Attempting to center circle in a varying curvature corner results in varying spacing between the circle and corner, which defeats the whole point of why different windows have different corner size (not calling it radius because they are not circles).

When the top right corner contains a search field instead of rounded button, that also seems to use varying curvature instead of capsule with proper circles at the ends. Still results in varying spacing between window corner and the toolbar content.

And that's just the 2 top corners. Attempts to align top corners result in even bigger mismatch with the rest of the window content. For example calculator -> it has a grid of round buttons. While the window corners might match top bar (as good as they can due to different shapes) the main calculation buttons don't match the corners at all.

Similar problem affects many of the popups which have something like confirmation button anchored to bottom right corner.

Rounded scrollbar handle - not aligned with bottom left corner size, instead it awkwardly gets cut of by different amount in each program.

Menus also have this disease. The non circular corner curve of overall menu shape extends way past the corner of item highlight resulting in varying spacing and making it feel almost like whole menu has bulged out instead of flat sides.

Exactly!

And to OC you're replying to: window close/minimise/resize were already equidistant from window edge on macOS 15 and probably earlier.

Here is a screenshot (safari in the background, textedit in front): https://pasteboard.co/OeMBTDKGsTx9.png

In MacOS 26 it's only weirder, because as you say - due to squircle window corners, now we have this constantly varying distance to the edge.

EDIT: I "get" apple's fascination to squircle, but why they made it such a big radius. Probably no one would've complained if they just have changed from current ~15-20px rounded corners into ~15-20px squircles, but they went 50px+ on toolbared windows.