Does it work if you unplug and replug?

In general, yes.

If you hit a button other than power does it wake up, or does it say “no signal” or something?

Yes.

Does the laptop see it?

I’m assuming not as it does not display on it. Next time it happens I’ll see what xrandr says.

Anything in any log?

Nothing in Xorg.0.log and nothing that seems related in the journal. I’ll keep journalctl --follow running and see if anything that I didn’t pick as being related comes up next time it happens.

Can you force a redetection from the laptop?

Probably, but I don’t know how.

1. If you use the same USB port for this all the time, disable power saving on that port

I use the same port all the time. I want power saving on the port. I like to just get up from my PC and have it go to sleep by itself and wake back up when I come and jiggle the mouse. It’s working exactly as I would like maybe 90% of the time. Just sometimes the external monitor doesn’t wake up.

2. Make sure this isn’t a PD port (this is a laptop design annoyance)

It is a PD port, and it is powering the laptop. I’m not sure why this would be a problem? It’s worked fine for 5-6 years with Windows and works 90% of the time now with Linux.

3. Make sure your monitor’s own power saving settings aren’t the issue by disabling things like “deep sleep” or similar

Again, I’m not sure how this could be a problem for the scenario I describe. The settings work fine 90% of the time. It’s not even time related: sometimes I can come to it first thing in the morning, after it’s been asleep all night, and it wakes perfectly; sometimes I can get up to go get a glass of water and come back and the external monitor won’t wake up. It seems totally random.

100% agree, which is a shame because having real numbers for the proportion of the population that don’t fit into what the bigots think is normal might help to convince some of them that they’re not so normal. (I’m not saying this very well, but I think you get what I mean.)

Beauty is in the eye of the beholder :-)

OK, I was on my phone. Just checked on my desktop and agree the original could do with some margins. I stand behind the rest of what I said - the default colours for the “best” are awful - the black black and red red is really garish. If I didn’t notice the dark/light mode switch and contrast adjustment does it really matter if they were there or not? There is also way to much information on the “best” one - if I’m going to a web site cold, with no expectation at all of what you might find, I’m not going to sit there and read that much text - I need a gentle introduction, that may lead somewhere.

I prefer the original. The “better” one had a bit of a lag (only a fraction of a second, but in this context that’s important) loading and the “best” one has the same lag and unreadable colours.