Uhhh, that was really fast! Hopefully it will work... ;)

Thx for your feedback. When I am using it a few days I also found some smaller problems, specially when I connect or disconnect my Display. Then I also have to change some Settings again. So its not the best way, but I can live with it...

Its a little bit tricky and not really perfect , because you have to play a little with the settings, but at least it works fine. With separat displays and not only mirrored. I have the first Macbook air M1 from beginning of 2021 and an IIyama 34" Display with native 3440x1440 resolution working now with HiDPI. I am so happy now!

Yes, you can buy this very cheep solution: https://www.apple.com/de/pro-display-xdr/ :-D

Lucky guy! ;) For me this solution was not working. Bought also the Adapter but it changed nothing...