[pjmlp]

WinUI uses COM/WinRT, COM is an OOP ABI, and WinRT is basically COM v2, with TLB libraries replaced with .NET type system and types must support IInspectable in addition to IUnknown. Are you going to argue .NET isn't OOP?

As for the rest, OOP doesn't imply inheritance, BETA and SELF are good examples of OOP without inheritance.

[ncmncm]

Nobody uses Beta or Self. And, no matter how much alphabet soup MS throws at its long, rolling UI debacle, it demonstrates nothing about general programmers' current level of interest in OO.

[pjmlp]

Arguing against industry usage of OOP, including C++20 own standard library, trying to fit one's little window of the world, also doesn't help.