Actually the problem is, the M1 does not support three monitors. The M1 Mini and all the M1 laptops support two. Most people forget to count the internal monitor on the laptops. (I know, the laptops don't support two EXTERNAL monitors but all that takes is one simple mistake with a hammer to fix.)The M1 mini does support dual monitors. The laptops only support one external in addition to the internal display.
Edited to say, I was just about to get a couple of ultrawides form my M1. I guess I will put it off a bit.