In practice it stopped working well long before windows 11 because so few apps were win32 based and/or because developers would explicitly override the theme. I

In practice it stopped working well long before windows 11 because so few apps were win32 based and/or because developers would explicitly override the theme. I gave it a go on Windows 7 and even apps like outlook and office wouldn't look right. Gnome/KDE still offer proper themeing that works with proper native apps but even there you've got web browsers and electron apps that ignore it.