Hey there. Just tried the shortest cable I found at the office. A ca 1m USB-C 3.1 cable from Samsung. No difference though. But found another solution. If I plug in another charger in my Macbook then my monitor turns on with video=) So, I guess just the PD Is not working as intended in Monterey.
Tried my other Macbook Air M1 with Big Sur and everything works with my old cable.