91.79 (1080p on a 24" monitor) is a good standard. try not to go below.
Therefor over 24" you should up the resolution. the next step is 2560x1440 (1440p) on a 27" - thats a high PPI of 108.79, some people need to up the scaling to see font, icons etc as they become smaller.
Upping the monitor size further we get to 32", keeping the same resolution of 1440p this comes back round to the exact same PPI of a 24" at 1080p - 91.79. Everything is perfectly sized, application & web, fonts, icons etc at default scaling of 100%.
The prob with high resolutions is that they need more GPU power as there are more pixels to push. If you can afford a good GPU then i advise you to go with a large 32" 16:9 monitor at 1440p. PErfect for gaming and other pc use such as work, video and browsing (which 21:9 suffers in comparison)
Note: 4k has incredibly high PPI & resolution but no GPU can run it fluently. Thats why its advised to stay at 1440p for the best gaming.