Thank you for the recommendation! I have, at this point, probably five forms of HDMI splitters, including at least two receivers (though admittedly no stereos). Unfortunately, I haven’t been able to get any of them working with the TV. I think, though I can’t confirm, that HDCP is the problem. The best I’ve managed to do is a multitude of sources plugged into the the splitter, but only two of them working; specifically my (original) switch and (also original) Steam Deck seem to be pretty recalcitrant.

I’m hoping the problem is the splitter / receiver. The new one, which promises HDCP compatibility, is set to arrive in four days. My fingers are metaphorically crossed. I’ve already replaced everything else but the consoles, so the next troubleshooting step, replacing the consoles, would be much more expensive.