M1 limitation is that it can support a total of 2 monitors. That means an internal monitor (if you have a MacBook/iPad) and 1 external monitor = a total of 2 monitors.

That is the reason why Mac Mini does support 2 external monitors - it does not have an internal monitor that "takes one slot". So you can connect 1 monitor to the HDMI port and 1 monitor to USB4.

I've been using SwitchResX for many years now, which enables all kinds of resolutions. It also works on my M1 iMac with a monitor connected via DisplayLink. Give it a try!

it works but with M1 and displaylink you get no HiDPI options above 1920x1080. On a 4k monitor the text is very large. On native 4k the text is very small. Using switchresx to other options results in 'low resolution' and the text on a 4k monitor is visually blurry.As displaylink have not offered any responses to the Dec2020 product request to provide other HiDPI options one can only guess if this limitation is displaylink or Apple. The only real apparent option for usability of a 4k monitor is a single monitor directly from the M1 without displaylink as this provides the missing resolutions.