https://bugs.winehq.org/show_bug.cgi?id=55789
--- Comment #7 from Fabian Maurer dark.shadow4@web.de --- I use chrome (and kde). I got it to work manually. Register mime-type, then open browser in terminal, open website, get "unknown protocol error", copy url from terminal. Then run
wine 'C:\Program Files\Steinberg\Activation Manager\SteinbergActivationManager.exe' --redirect "net-steinberg-activation-manager:/login/oauth2/code ......."
Not sure what exactly is wrong, but it works now, will test soon.