M1 Macs can handle up to six external displays via DisplayPort adapters — Apple World Today

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.