> For 2008 the style was quite good looking
Not really. It doesn't look good now, and it didn’t look good then. It's just not good-looking.
For comparison, Leopard/Snow Leopard looked good in 2008, and it looks good now: <https://en.wikipedia.org/wiki/File:Leopard_Desktop.png>
Among the things that I find really surprising in the computing industry is that everyone doesn't make things easy for themselves and agree to just rip off Cocoa.
On the one hand, we hear every time that Electron or the Windows/.NET UI framework discussions come up that developers have no good choices for doing cross-platform UIs. Meanwhile, Cocoa's API is no more or less protected than the ones that Sun/Oracle went to war over. It's also extremely mature. So make it easy and just rip off Cocoa already.
On the other hand, Apple have moved to flat, mobile-like UI. There's hardly a case to be upset, then, if someone were to show up with a lookalike of the old, decrepit Mac OS visual style—something like Aristo <https://www.cappuccino.dev/aristo/>. So make it easy and just rip off Cocoa already.