2D game aspect ratio (vision range)

Hi, a really dumb question is incoming.

I just wanted to ask how changing the aspect ratio affects a 2D game.
At the current state of our game the user is just able to pick screen resolutions that are 16:9, because I don’t know what exactly happens otherwise. Ofc I’m not quite satisfied with that solution.

So, let’s say person A plays our game with 16:9 and person B with 1:1 ratio. Where would be the difference? Would B see the picture distorted? Or would A have a wider range of vision horizontally, while B would see more things vertically? And if one of those things is the case, how to fix it to avoid possible bugs?

You can test what happens yourself if you go to Edit->Editor Preferences->Play. And then inputting a custom screen size for Play in Standalone Game etc.