How did you install Screen2Auto?
Easiest way that works with both of my non-rooted phones is to install AAEASE, then open it and install Screen2Auto. If this is what you already did, you might try uninstalling, Android, Auto and screen to auto and starting over, making sure to give all permissions to screen to auto app.
Wasn't clear from your posting but you have to open screen to auto on the phone first and give it permissions before you can use it through Android Auto. Waze is still not going to work in your case though, that's apparently due to Android 8.
I have used this procedure, but I don't see Screen2Auto in Android Auto. I'm mainly concerned with Waze, everything else works. With Android 8 is there no chance? In Android Auto 7.7 everything worked, but here you can't use it because of force update from Google.