That's correct, as long as your channel scenes are based on an FHD (1920x1080) layout. If so, and you don't specify any other resolutions, the channel should automatically scale if running at a different resolution.
To be clear, belltown's comment is about `ui_resolutions=fhd` setting, which is completely independent from the icon and splash screen settings. That is, if you design your UI layout for `ui_resolutions=hd`, it will still get re-sized to the actual screen resolution - and that has no effect to the icon/poster choice.
Nor does the choice of ui_resolutions
affect the video resolution. That is, a 4k video stream will play in 4k on device with Settings > Display type = "4K UHD... ", regardless if you chose to position your UI elements in SD, HD or FHD units