SOLVED FOR ME: apologize…
Removed a previous used Registry-Tweak an now it works (DLSS is showing up now). Credits goes to much_0_ado on "VRFlightSimGuy`s Discord:
The Tweak was to add a Key named TdrLevel in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\GraphicsDrivers.
So I reverted this tweak and now DLSS shows up.