Usually when I get the flicker I have to do the following:
- I disconnect the USB-C adapter and only connect one monitor through the HDMI port. (No USB-C should be connected to any of the ports).
- I reboot and login to the system (only one monitor connected)
- Once logged in, everything should be working fine with one monitor
- I connect the second monitor by plugging the USB-C connector.
- The second monitor should display fine and both should work until next time you reboot or put Mac to sleep.
*if this doesn't work, then I do the exact sequence but starting with the USB-C instead of the HDMI.
***** this is happening to us. I'm still not sure if it is a Mac issue or adapter issue.
Earlier today I noticed this on the Mac mini specs page:
Simultaneously supports up to two displays:
One display with up to 6K resolution at 60Hz connected via Thunderbolt and one display with up to 4K resolution at 60Hz connected via HDMI 2.0
Thunderbolt 3 digital video output supports
Native DisplayPort output over USB‑C
Thunderbolt 2, DVI, and VGA output supported using adapters (sold separately)
HDMI 2.0 display video output
Support for one display with up to 4K resolution at 60Hz
DVI output using HDMI to DVI Adapter (sold separately)
So maybe Mac mini doesn't support connecting two displays via HDMI, maybe one has to be Display Port as the specs do list it as supporting 'Native DisplayPort output over USB‑C".
I'll ponder about buying a USB-C to Display Port adapter to try.
For now I'm just using one monitor since I don't want to be disconnecting/connecting cables each day...