I don't know if it's #Debian 11, or my hardware, or because my house is under a wicked spell, but if I switch my "tv" away from my "tv server" it now disables that display and doesn't enable it if you switch back. nothing less than a reboot seems to do that.
Still don't have anything like a working #mythtv. after all that work – debian 11, latest mythtv – it's the same. so I suppose a cap must have popped on the motherboard or something; that's all I have left (unless wicked spell, which…)