This is a fairly technical meme. Userspace is not the same as user preferences, and in this case refers to application compatibility. Applications written by third party developers (i.e. not the creators of the OS itself) are almost always in userspace and not kernelspace.

Windows and the Linux Kernel devs go to great lengths to ensure that they are backwards compatible, sometimes to a fault. For example, there are certain bugs that are left in place and not fixed because some applications have adapted to the bugs and now rely on that behavior. If the bugs were fixed, suddenly those apps would break and the developers of those apps would need to create an update. That's complicated or even impossible if the app developer has been out of business since the 90s/dies/is locked up in legal limbo/etc.

You can still run games and other software from the 90s on Windows 11, but there is software from the 2010s that won't run on the latest version of macOS because Apple doesn't give a fuck about maintaining backwards compatibility (breaking userspace).