There was a golden period of OS X roughly between 10.5 and 10.9.

Up to 10.4, windows were too textured: stripes, brushed metal.

In 10.5 till 10.9 we got to enjoy the beauty of Aqua paired with calm, tasteful gray window frames and controls that had visible depth.

From 10.10 till 10.15 was okay-ish: the flat took over, but we still had contrast and shapes.

Starting from 11, everything became rounded, low contrast and lost visual cohesiveness.

10.5 till 10.9. We didn’t know how good we had it

@nikitonsky 100% agree.
The iOS influence is bigger every day and this is slowly killing the quality (UI side) of MacOS.
Shallow? If you struggle to understand the purpose of a UI component this brings an additional mental charge. And this matters. This disease also touched Windows which I had to use at work. This low contrast and absence of clear recognition of each UI component coupled with virtual machines was a nightmare.