Odd monitor issue.

[claydoh]

A hardware bugaboo unrelated to any operating system:

I have an Acer SB220Q monitor that for some odd reason refuses to work on during POST or to get to my firmware settings.
This happens no matter which GPU it is connected, whether it is the onboard Intel igpu, or after adding an AMD RX 480, or my previous RX 560. Swapping cables, or even using an HDMi-DP adapter does nothing.
I have to use the TV (connected as a part time second monitor) to access the firmware settings, boot options, or grub. Even there, it sometimes does not show there, unless it is active and running when I reboot, or if I do a cold boot. I think.

Past grub, it works fine. I do get a [not supported] message on the monitor screen during boot

I have reset the monitor's settings.

I wonder if it is something on the PC (HP Pavilion 590-p0097c i5-8400)
The firmware settings are fairly minimal, being a home computer so there really are not many settings. I have tried resetting the firmware to stock default settings.
The Intel graphics are disabled when the discrete GPU is attached.

Looking for any brainstorm ideas, as my research has not revealed anything useful.
It is nothing important mind you, but a minor annoyance.

[Snowhog]

Does the anomalous behavior present if you boot from a LiveUSB? Might be telling.

[claydoh]

Yes, when I installed Neon when i got this PC a few months back. Have not tried it again since, though. It was how I discovered the oddity.
it is strange that it (usually) works with the TV. The acer does this even if it is the only device plugged in.

I may need to find out about clearing the cmos as a next step.

[Qqmike]

Looking for any brainstorm ideas

Clearing the CMOS sounds good.
And/or
Checking "BIOS" updates at the motherboard website.

I had something somewhat similar, never did pinpoint cause exactly, but after re-installing the whole BIOS, it sure seems like BIOS contamination. It just smells of a BIOS issue.