Apparently the M1 can support an external plugged monitor and an iPad via SideCar. Not a big monitor, to be sure, but it's not nothing. [1]
Edit: ... and having said all that, I'm looking forward to upgrading some time in the next year and going back to two "proper" external monitors. I'll still love using the Sidecar'ed iPad Pro as a second screen when working in cafes, though...