AVNC is open source and it at least has a mini keyboard where you can queue Super to be held with your next keypress
https://f-droid.org/en/packages/com.gaurav.avnc/
If you're using a USB or Bluetooth keyboard, it's probably not possible for you to use your actual super key on it. That gets translated to "Home" in Android which is why you go back to your launcher. For whatever you're trying to do, software keys is probably the only option.