I don’t think Fdroid can specifically differentiate Android TV devices. What you might be able to do is have two different versions with different minSDKs on F-Droid which are relased simultaniously.
Devices which have sufficiently high Android version will be shown both app versions and can always upgrade to the higher minSDK one. Older devices will be shown only one version.
That’s far from pretty but should work relatively well right now.
(btw, I love NewPipe!)
E: If I understood you correctly that the that includes support for Android TV would be a superset of the ‘normal’ version. Otherwise this would of course not work.