Adding a second external display to my M1 iMac

Yes, although it worked fine until MacOS 12.3. Two external displays worked perfectly.

So I expect that a hardware solution is necessary (because I only need the Mac to see one display. It doesn't need to know that I really have two).

I will check them out.

I wonder if the posted limitations were so very close to what was needed that I could use two external HDMI ports (at least mirrored) until universal control used some more resources.

They have this product: https://eshop.macsales.com/item/OWC/CADPDL2HDMI/, that looks good for my needs. At $119, I expect to wait until the end of the month (and will return it if it doesn't work).

I noticed one of the features is on my $70 Apple HDMI card, the ability to recharge a Mac while using it. Not useful for iMacs like mine, I was hoping that that USB port worked the other way (to plug in a device).

I needed to install https://www.synaptics.com/products/displaylink-graphics/downloads/macos, and allow it in System Preferences > Security and Privacy > General. I couldn't figure out how to get it visible there, but after I rebooted, when I tried to run it, it automatically showed up. Now, when I run it with other monitors attached, they show up and I can configure it. I tested it out successfully. Since I run karaoke night twice a month, I won't set DisplayLink to run automatically.

I then booted to my clone external drive, and installed DisplayLink there. But I even with multiple boots, I couldn't figure out how to get it in System Preferences > Security and Privacy > General.

Tested it out. It has two HDMI sockets on one side and a USB-C on the other, similar to my USB external bus. And as with that bus, MacOS 12.3 doesn't see any of them.

Oh, I also tested the driver with my old USB bus that I used before MacOS 12.3. It didn't work.

It's working now. I'm not sure what I did.