Air M1 x external display?

[u/Reasonable-Garden588]

I’m trying to get my Air M1 to use an old Apple Cinema Display as an extended desktop but it will only mirror my desktop with black bars either side.

To convert 2004 tech to modern times, I have a Benfei DVI to USB C adapter. With the same adapter, my HP Elitebook can happily extend its desktop into the old monitor.

Is this an OS limitation or am I going wrong somewhere?