Peak windows was Windows 7 in both design and Function. It was pinnacle User Experience of a traditional OS before Microsoft started chasing fads, (Touchscreens in Windows 8, Cloud integration in Windows 10, and now AI bullshit in Windows 11)
No opinion on macOS. My only complaint is that its not linux.
Instead of Flatpak I would replace that with AppImages. At least with Flatpak I get some semblance of the SW Integrating with my DE and a semblance of a package manager. AppImages I feel like are like rolling the dice on how much effort the dev put into it.
I declare war on this hill!