Wired printer won't show up on Nighthawk R7000P

Thanks for your response, and for helping make the scenario more clear.

>   What does "printer cable" mean to you?  Parallel?  Serial?  USB?
Other?

USB printer cable.

>   Which "the router light indicates" how?  I believe you, but a less
> vague description would inspire more confidence.

The light on the router is an orange light that occasionally blinks. It has the same look/pattern as the other two working connected devices on this router (a phillips Hue, and an Arlo hub).

>   History?  Is the printer configured with some wrong-subnet (static?)
> IP parameters?

I have had the printer for over 10 years. I don't recall if it was previously wired successfull as we have been using the USB printer cable for at least 6 years. Unfortunately I don't have a way of checking the ip configuration because there is no screen on the printer.

>   I'm too lazy to do the research, but I'd guess that it can be
> instructed (manually) to print a configuration page which would include
> its IP parameters.  I'd also guess that it could be reset in a way which
> would persuade it to use DHCP (again?), which might be enough to make
> everyone happy.

Thanks for pushing me in this direction! This printer has no screen, so the only way to see the ip configuration is to print a manual test page. But, for some reason the printer hasn't been able to print a test page in a long time (even though it works fine printing over that USB printer cable). It just clicks once when I try to print the test page and then does nothing.

So, I poked around a bit about this and found this: https://h30434.www3.hp.com/t5/Printers-Archive-Read-Only/HP-LaserJet-P1505n/td-p/2690 . TLDR; you can reset the network config by holding red/green buttons for 6 seconds while powering up. Once I reset the config I was able to print a test page, and now it shows up in attached devices in the router admin.

Thanks for helping me think of it as a printer issue :-).