I assume that if Microsoft hadn't abandoned WinForms for the next thing, it would support dynamic sizing and DPI properly. It's mindboggling how much time and effort they've wasted coming up with new GUI frameworks instead of just improving on what they have.

It's been a while since I've touched it, but IIRC they made WinForms play with Hi-DPI nicely.

Windows dynamically sized is quite easy, people have had enough time to learn how to use layout managers in Windows Forms.

Naturally it is a bit more than just drag and drop controls from the toolbox.

HiDPI is supported in modern .NET, with additionally APIs, that aren't enabled by default only due to backwards compatibility.

Or, unless they've changed it, hardware accelerated rendering. Winforms was based on System.Drawing, which used GDI+, which was largely software rendering. This was confusing because GDI+ was not really related to GDI, which had and still does retain some hardware acceleration support. Even basic color fills start becoming an issue with a big window/monitor.

Winforms is also .NET based, so it's inaccessible if you don't want to write your UI in and take a dependency on .NET.

transparency as well. WinForm really struggles with the idea of stacking elements on top of one another where there is an arbitrary amount of transparency or tricky shapes. Its just not worth the hassle compared to WPF.