I'm using a Mac Mini, dual BenQ monitors, connected via usb-c and running the latest public beta update broke dual displays (21E5196i). I tried the suggestions with power and such, nothing worked. I tried different USB-C ports, and discovered that only one port is working for video. I have a Caldigit ts3 connected to another usb-c port, it works, but video does not through that device.

No change on 12.3 Beta (21E5206e)

No change on latest beta (21E5212f). Also still can't get to the Detect Display button.

No change on 12.3 Beta (21E5222a), still only one monitor working. No 'Detect Displays' button either.

I tried turning off both monitors at the same time, turned them back on, and it switched to the other monitor. Makes no sense...

I have a Caldigit TS3 hooked to my Mac Mini, it has the latest updates. I disconnected it, rebooted, and still can only get one monitor to work. I saw a new developer beta dropped, I'll update to latest public beta once it drops and see how it goes.

Just updated to the latest public beta (21E5227a) and no change. This time I only had the two external monitors connected to my mac mini, installed the update, when it came back up there was no change. The Detect Displays button is also still missing.

No change on 21E230 - the RC for 12.3. Detect Display button still missing.

There are no changes with 12.3 RC (21E230). It will not detect a 2nd display, the ironic thing is I can get it to switch to the other display, so it's not a cable or display issue.

2018 Mac Mini - dual BenQ EW3270U connected via USB-C, made sure they were both plugged into separate Thunderbolt Bus on the back. Shutdown, took the kid to school, came back and booted up, no change. I plugged a DisplayPort cable into my CalDigit TS3 on both Thunderbolt Bus and still no change. I can't find in the menu to change this to DisplayPort 1.2 to try that. This is something that Apple needs to address, it was working prior to 12.3.

12.3.1 released today to fix the issues on the 2018 Mac Mini. I'm downloading and installing it now, I'll update this thread when it comes back up.

Can confirm this is fixed in 12.3.1, I have missed this setup!!!