That's on current WinUI/UWP XAML, the new version in preview (WinUI 3) pulls out components deeper into the stack so it can run a couple more Windows versions back (to 1803 I think)
Having actually tried to use XAML Islands to get some UWP UI controls into a WPF application, I can say that the experience was absolutely horrible and I ended up giving up and not using the UWP control after all. Truly, truly horrible.