Modern UI is a crime against humanity. I did not think there were new depths to the depravity, yet here we are. Society has been backsliding since XP.
I wonder if XP fondness dates you to a certain age bracket. Yeah new UIs seem disorganized and inconsistent to me but I feel the best consistency in UI was hit around Windows 95-98 but then again that's when I was in my young adult years. Maybe the kids feel this new crap is how UI should be done...
Some people despised the XP UI when it first came out to a lot of fanfare. To this day, "Fisher-Price UI" is strongly associated with it.
Most people seem to think that whatever design language they got used to at a certain age was the obviously superior choice for all ages.
I think the biggest issue of modern UI design is that a lot of the software with it is poisoned by metric-chasing and mass data collection that megacorps love. But on a deeper level, most modern UX designers are vastly better than the average person working on UIs in the 90s. All the horrendous stuff from the 90s got forgotten, leaving behind only the fond memories of Windows 9x and similar.
I'm much younger than you, and I get liking the 9x design only in the sense that this was the last time when MS did a clean-slate design and redesigned everything in the system to be consistent, as opposed to them juggling like 6 different design languages for the sake of backwards compatibility and their apparent fear of not making something new. But as a design.. well, "all components must be the exact same shade of grey, look identical and have as little hierarchy as possible" isn't the peak of design, imo.