I have no direct personal experience on high-DPI macOS. For Windows, I’ve only come across a couple of apps that claimed to support high DPI but severely mangle

I have no direct personal experience on high-DPI macOS. For Windows, I’ve only come across a couple of apps that claimed to support high DPI but severely mangled it, and they both got fixed before long; and a few others that had minor problems, e.g. opening windows at unscaled sizes so that you had to resize them, or rendering small icons. And to be sure there are various DPI-unaware apps, probably far more than on macOS (linked to why Apple was in the perfect position to implement and impose proper fractional scaling), but that’s not a serious problem either.