The short answer is, sadly, no— Apple has the modern macOS UI locked up.
The long answer is, if you're willing to disable systemwide security features, you can experiment with modifying the appearance of macOS, but to my knowledge no one has made a real attempt to in a while. Furthermore, the themes on display here fit a paradigm where the UI is a composite of bitmap images, whereas the modern macOS is largely built from vector graphics.
But if you vectorize every bitmap in an old theme, so that individual pixels of color are converted to vector graphic rectangles; if you learn how modern macOS builds its appearance; if you make a robust solution and thoroughly test it, so that it will work 100% of the time with every app ever; if you do _all_ of that, you will still be unable to _share_ your creation with most Mac users, because very few of us would disable systemwide security for the sake of running a third party system enhancement.
That's one of the major contributors to the success of Mac OS 9 theming: third party system extensions were commonplace, they were the backbone of the ecosystem, and Apple had no mechanism for preventing their use.
1. Kaleidoscope (the most common OS 9 theme system extension) runs fine under emulation, so if you just want to _enjoy_ these themes, your best bet is the SheepShaver emulator (in my opinion).
2. Nothing's stopping us from creating an alternative desktop environment for the Mac, such as XQuartz. And then you can build theme support on top of something like that. But most applications wouldn't use that desktop environment for their own UI.
> Nothing's stopping us from creating an alternative desktop environment for the Mac, such as XQuartz.
Yea but why use a mac at that point? I don't see anyone on the linux side of things making anything that acknowledges why people use macs in the first place; the entire ecosystem is built to reproduce the IBM PC (...in a unix/like environment). Particularly with its disastrous keybindings and perplexing UI decisions.
The pipeline from Windows to Linux is fairly clear. The pipeline from Mac to Linux is less evident; the dyed in the wool Mac users tend to stay that way, using Linux for work rather than a daily driver.
Queue a Mac-to-Linux user to contradict this, and there's plenty of them, but we Mac users are truly the dictionary definition of the sunk cost fallacy in more ways than one.
It doesn’t help matters that desktop environments that try to do things “the mac way” and don’t just mimic macOS superficially (like Pantheon/elementary) don’t exist. Everything is either Win9X-like (KDE, Cinnamon, XFCE, LxQt, etc) or tablet-like (GNOME). For the most part, to a longtime Mac user switching to Linux feels like switching to a bizarre alternate universe Windows that’s built around the Linux kernel instead of the NT kernel.
Apple hardware quality is just orders of magnitude beyond what competitors do. The day this stops being true (whether because Apple slips too much, or because competitors step up in major ways - not sure which is likelier) I expect we’ll see a lot more Mac-to-Linux migrations, with the virtuous circle kind of benefits that this can bring.
> The pipeline from Windows to Linux is fairly clear. The pipeline from Mac to Linux is less evident; the dyed in the wool Mac users tend to stay that way, using Linux for work rather than a daily driver.
This has been my own observation as well. Although I do have to say, System76's COSMIC DE has been the first one that is actually making me consider going to Linux full time since I've switched to Mac from it. macOS has only been continuing to annoy me more and more lately.
The problem for me is hardware. Asahi isn't there yet, and I'm not giving up my M4 Pro MBP. There's no other laptop on the market that checks all the same boxes. But for now, I've just bypassed the mac's weak points by using Aerospace, and if I'm honest with myself I don't want to give up the ecosystem integration either.
I ask myself that with increasing frequency. Looking at all the Linux options feels like wandering through Akihabara, but one day the macOS that remains will be so unlike the macOS I enjoyed, that I'll jump the fence.
Anyway, if someone does make a new Mac desktop environment, it'd probably be for fun more than anything. Or a Terry Davis scenario.
