In case you have switched to the new Chromium-based Edge, you're in luck because the same shortcut trick of bringing back the original Windows themed titlebar used for Chrome, works here as well!
All you need to do is right-click your Edge shortcut (either on the desktop or the taskbar) and add the following parameter to the Target property " --disable-windows10-custom-titlebar" (without the quotes but with a space before the --) and hit Apply.
Now every time you start Edge it will show up with the nicely themed titlebar, which looks something like this:
with my Simplify Darkish Theme applied. Pretty cool, right?
Enjoy and thank you for all your support!