Mac Mini - HDMI Monitor issue

[iggibar]

I have extensive experience with Macs running on multiple monitors, and especially with the base M1 and M1 Pro. Base M1 and M2 chips are the most problematic. M1 Pro+ and M2 Pro+ are much better at managing displays.

Your M1 Mac Mini can't natively support dual monitors without one monitor using an actual USB-C monitor input. There just is not enough bandwidth and power to support 2 alternate connections and adapters. On top of this, the base M1 and M2 are SUPER SENSITIVE to adapters and video cables from decades ago. The use of these adapters gives the M1 chip an inability to sense screen resolution through them. All Apple computers automatically sense screen resolutions upon startup and sync to the screen. If you have seen screen flashes, you have witnessed this process. When the resolution sensing times out, you get what is commonly seen as black or fuzzy screens. Sometimes these setups appear to work, but then show their issues when bandwidth limits are reached, or there is a sync/resync issue during wakeup.

On top of ALL that stuff, there currently is an issue with all M1 and M2 chips related to video and display issues that is specifically linked to USB-C/Thunderbolt. There has been no fix yet, and no definitive explanation or knowledge of how extensive this issue is.

From my experience, I have found that the most reliable and best way to go around these issues is to buy a display hub and then install "DisplayLink Driver" on your Mac. The hub provides multiple outputs for screens and peripherals. The driver works to manage your bandwidth going out to your hub and allows you to be able to properly send video signal to whatever screen you have. This will take care of all your resolution syncing issues, screen sensing issues, and bandwidth issues. Works really well!

 

[Jimmysb]

So back to the HDMI issue; the "static" screen only appeared after the Mac had been asleep (which components were asleep - I don't know), and only occasionally, and switching the monitor off then on would remedy the issue. Having the monitor switched off, waking the Mac and switching on the monitor had no issues. As said in the initial post, this never occurred when the same monitor was used with my Win PC or my works Win Laptop, however, on consideration, I am not sure if the same situation occurred, i.e. either them gone to sleep.
So thought something from the Mac is (IMHO) a partial contributor, switching off and on the monitor would also suggest a monitor issue. Moving forward, looking through the monitor settings, I notice the monitor display setting were on auto switching (due to how the monitor was used for work/home), I have now set this to HDMI, and the first thing I notice is that the monitor wakes quicker, and currently the issue has not occurred - yet!!
My thoughts are when the monitor is wakened on auto, though it is getting the signal to wake, it is not always interpreting it correctly, leading to static, but switching off/on, gets the correct signal and works. With auto off this should not occur, time will tell.

 

[Slydude]

That's a good hypothesis. I used to have the same/ a similar issue with an adapter used to connect an HDMI monitor to my iMac. The behavior seemed to be really hit or miss and similar/identical to what you're seeing.