M1 Macs can only output two video signals at once, so your options are splitting one of them using an external box, or generating a third signal using a USB graphics card.
The latter are mostly (always?) based on DisplayLink, which has spotty support by Apple, though some people seem happy with it.
Ok so that sounds like I could have main display to the hdmi port, then get a splitter to plug in to a usb-c and have the two displays (2nd screen plus cintiq) mirrored using the splitter?
M1 Macs can only output two video signals at once, so your options are splitting one of them using an external box, or generating a third signal using a USB graphics card.
The latter are mostly (always?) based on DisplayLink, which has spotty support by Apple, though some people seem happy with it.