Using a MacBook Air as a second monitor

Good day

I am replying to an older post from 2016 by "brunofromcapetown" https://discussions.apple.com/thread/7701694.

Unfortunately, I have not found anything to see if there is another solution. Like "brunofromcapetown" many appelfriends have this problem. So do I. It doesn't seem to be possible to use my "MacBook Air, early 2015 (13", I7, 8GB, 512GB), wireless or via Thunderbold, as a second monitor.

I recently bought the "MacBook Air 2020 M1". Since Excel still does not support all functions under M1 and various functions crash under Rosetta, the older device must remain in use. Also, for ecological reasons, I am not prepared to buy a new screen in order to use it only rarely. I can't believe that Apple has so little ecological conscience and would force its customers to dispose of a perfectly functioning device instead of allowing it to live a second life as a monitor and backup computer.

Unfortunately, my English is not good and the German-language pages do not provide a solution. Therefore, the text has been translated with Deepl and I am trying English language sites.

I hope for your support and solution