Using a USB-powered DisplayLink adapter. That's it.
M1 chip's GPU only supports two total displays. One over the Thunderbolt bus, and one either internal (for the laptops) or over HDMI. On the Mini, if you want two displays from the M1's GPU, one has to be plugged in to the HDMI port.
The only other options are "software graphics" - SideCar to an iPad, AirPlay to an AppleTV, or DisplayLink. They use up CPU just running the display, generally don't perform well with 3D or fast-motion (video). They're generally fine for text, though.