Dual monitors for M1 Mac mini

https://www.apple.com/mac-mini/specs/

Depends on your 1st monitor's connection type. M1 Mac Mini dual monitor support is via TB3 + HDMI.

If you used HDMI for 1st monitor, then you have to use TB3/USB-c for 2nd monitor.

If you used TB3/USB-c for 1st monitor, then you will need HDMI for 2nd monitor.

Please check the second monitor's spec and available input port (DVI? Display Port? Thunberbolt Port? ..etc) - in order to find the best connection (or need adapter alike).

Oldedit wrote:

...I can attach a 2nd monitor with a cable that has USB C on one end and a Thunderbolt 3 on the other without an adapter.

....

There is no such animal. USB-C is a connector specification and does not define the signals carried on it.

With that said, there are Thunderbolt 3 cables and there are USB-C cables.

If your display has a USB-C interface on it, you can use either cable, though a USB-C cable will be cheaper.

Or if the display has HDMI or DisplayPort, you will need either a USB-C adapter to those interfaces or a cable with USB-C with HDMI or Display port ends. There are literally hundreds of these to choose from, just search Amazon.