The integrated graphics on the M1 chip support only two displays, one at up to 4K and one at up to 6K. On the MacBook Pro/Air, the lower resolution one is dedicated to the internal display. The M1 Mini can support two external displays because there's no internal one.
Your Mac can drive Apple's beautiful (and expensive) 6K display, but not two external displays.
Apple states clearly in the specs for the M1 notebooks:
Video Support
Simultaneously supports full native resolution on the built-in display at millions of colors and:
- One external display with up to 6K resolution at 60Hz
Personally, I read the specs on a computer before I buy it and I don't buy it unless it meets my needs. If you require two external displays, buying an M1 notebook was not the right choice.
One option to consider is an ultrawide or super-ultrawide display. Personally I have a 5K:2K ultrawide that gives me close to two displays' width; there are 49" super-UW 5120x1440 (32:9) displays that are equivalent to a pair or 24" 16:9 displays.