Because he doesn't have an M1 iMac?Why not just check the displays preference pane?
If I buy you a (very cheap) copy of Resolutionator, could you note for us some of the extra resolutions it enables?the larger text option says: 1280 X 720
the next one up says: 1600 X 900
the next one to that/one lower from default says: 1920 X 1080
The default selection says: 2240 X 1260
the more space option says: 2560 X 1440