Qt had what is essentially flexbox in early 2000s.

Native apps have had to deal with dynamic sizes and layouts since the idea of resizing windows to arbitrary sizes became a thing. So, since 1980s?

> on-the-fly resizing

Which web tech famously cannot do with any efficiency

> and layout of multiple complex screen sections

What complex screen sections? This is a complex screen section: https://x.com/dmitriid/status/1424052288205856773

The web does not (and cannot) have "complex screen sections". It doesn't have the capacity for it.