OK this is more of a specific response, mainly to anyone attempting to connect TWO Apple 30" (maybe other sizes too?) Cinema Displays to an M1 Mini. I am writing this all to document for anyone else in the hopes that they don't have to jump through all the hoops I did, also for my own reference later as the issue is not resolved!
Bought a new M1 mini (16Gb of RAM) in January; after reading SOME threads and watching a couple YT videos (like the one where the dude hooks up 6 monitors), I was confident that it would take some trials but all I had to do was figure out the right set of adapters and I'd be golden.
My monitors are the older ones, not Thunderbolt, so already were running to my 2013 Mac Pro via the expensive dual-link minidisplayport to DVI adapters. I tried this HDMI cable before my mini even came, no dice so I sent it back.
Then came the onslaught of attempted cables, some using the minidisplayport adapter and others including the Startech USB adapters that have their own GPU card.
Didn't work: this this this this and this
These 2 USB-C/Minidisplayport adapters DO work, at least in connecting ONE of the monitors:
https://www.amazon.com/gp/product/B01N4FQNYW/ref=ppx_yo_dt_b_asin_title_o02_s01?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B08B7FSVTL/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1
Finally discovered Apple had an HDMI-DVI adapter, so had to try that, right? No dice, sent it back.
Then I moved to the DisplayLink software route, trying this Startech adapter as well as a single display adapter(using another adapter in the middle, which seemed to work but then would fritz out. Then it really just wouldn't work.
Oh also forget trying to sleep the computer and then hoping the displays would wake up too, I would always have to re-plug in the cords to get anything to show up. I spent time in Safe Mode, Recovery mode, tried changing the desktops (now there's this new adaptive desktop that changes sunlight throughout the day, could that be it?--eventually figured out, no that's not the issue). Note that this is pressing option while changing the resolution in Displays system prefs to toggle different things here and there, trying all kinds of combinations and forgetting which ones I'd tried and then trying them all again. Oof.
Then I read that 11.2 fixed the displays problem! Oh, the problem was actually in the OS?! I guess I had given Apple too much credit and assumed it was the adapters. So I pre-emptively rebought that Apple HDMI-DVI adapter, giddily updated, and upon hooking it up--it... didn't work.... but now I COULD get the HDMI-connected display to come on in lower-res mode, at least on startup.
I kept reading more and more, but could not get the 2 displays to come online at once, ever, for more than 5 minutes. So I finally scrapped the notion of even trying for 2, but then read this article about resetting the color calibration, so I tried it.
I had already tried creating new calibrations settings (I thought), but wth ok, I gave it a shot: and lo and behold, the 2nd display (connected via HDMI) would come on! ...so long as I left it in 1280x800. Tried a lot of other things to no avail, and FINALLY called Apple.
Got escalated, and spoke with a tech who spent some time looking through Engineering notes. Came up with the pronouncement that 2 Cinema Displays will NOT work with the M1 mini, at all. !! Wait what? I told him that I was seeing the second monitor, so long as it was in 1280x800 (or less), and it did appear stable. He said that according to Engineering the company is surprised by that. We ran through a number of alternatives most of which I had tried, but apparently the company believes I should not be seeing ANYTHING on the 2nd monitor. Welp. OK, he wrote it down, said they may call me back, and here I am, still enjoying these monitors and hoping for an 11.3 fix (not holding my breath).
So, to recap, I am using one display connected via USB-c to minidisplayport to minidisplayport-DVI adapter, and the other is Apple's HDMI-DVI adapter right to the DVI connection (with all USB 2 cables plugged in too). I sent back the DisplayLink gear after the tech I spoke with said that it was a dead-end, that anything with an external GPU was uncharted or dangerous waters in terms of the M1 chip. And I have 1 and a half working displays. (OH btw I DID try using a different monitor via an HDMI cable, it worked fine 1920x1080 so at this point I think the dual-display issue (so long as it's not 2 ACDs) is solved in the 11.2 update, at least as far as I can see with a basic TV monitor via HDMI along with the aforementioned USB-C connection to my ACD)
I'm sure I forget a whole set of attempts to fix this, but I hope this helps someone. Or Apple to fix whatever the bug is. Til then I'll limp along with my half monitor and consider buying a new one (but I LOVE these old LCD monitors! so little glare!). Good luck.
