[jubilex]

Yeah - only one mode available for you. For me it shows all available modes TV / AVR have.

So that seems to be an issue between my Fire TV and my AVR that I'll have to find a solution for, or give up and go with Rpi4. 

Any ideas about the issue of 2.40 aspect ratio trailers being stretched vertically to 16:9? I can't think of a reason for that since 2.40 aspect ratio full movies display correctly. And this, too, happens only with my Leia installation on Fire TV 4k and not my Leia installation on Rpi3/Librelec, running the same version of Cinemavision add-on and plugged into the same AVR and displays.