The specs on the M1 Macs just keep getting more impressive. It seems you can run up to six external displays from the M1 Mac mini, and five external displays from the M1 MacBook Air and MacBook Pro, with the aid of DisplayPort adapters, according to YouTuber Ruslan Tulupov (as noted by MacRumors).
Apple says that the M1 MacBook Air and M1 MacBook Pro can run one external display with up to 6K resolution at 60Hz. The M1 Mac mini can run one display with up to 6K resolution at 60Hz connected via Thunderbolt and one display with up to 4K resolution at 60Hz connected via HDMI 2.0.
However, Tulupov has found that you can run as many as six external displays from the M1 Mac mini, and five external displays from the MacBook Air and MacBook Pro. This can be done via a workaround using DisplayPort adapters ad DisplayLink software to drive the additional displays. When the M1 Mac’s ports have been filled, DisplayPort adapters have to be connected via an external dock to provide more ports.