It's interesting because that thread says that Windows 11 kills Curtains but I actually have Curtains running on my Windows 11 computer and it still works. It was installed on my Windows 10 so when I upgraded it was already there. Unfortunately, I receive weekly notifications that there is an update to Curtains but it won't allow me to install it because it says that it is not compatible. I wish I could go ahead and install it just to see what happens since it is already running.
Whilst it may be running it isn't actually working correctly.
You do not have custom titlebars (other than the min, max, close and on universal apps), you do not have custom taskbar (unless you have Start11). All you really get is accent colour and wallpaper changes.