Behodar:
Sudden failure of an HDMI cable that's been happily sitting untouched behind the TV for two years.
Next annoyance: Realising that that was a bad diagnosis. There's nothing wrong with the cable. I turned the PS5 on yesterday and there was no video. I connected a different cable between the PS5 and the TV (same port) and it worked. Conclusion: Cable is bad.
In reality, a couple of days ago I unplugged the PSVR box at the wall since I haven't used it in ages, completely forgetting that the HDMI runs through it. I'd accidentally bypassed it when testing yesterday...