@pixelfed looks good, I'm going to look into setting up an account now!

I've seen a few calls for allowing users to change the way in which images are displayed, which ratios to use etc.

I'd say this will probably be an impedance for creators who decide to start producing work for pixelfed in the same way they might for Instagram.

Having a guarantee about how your work will be displayed to others allows you to make informed choices about composition, sequencing, etc. This is the reason design for print is often much more exciting than the web. The interplay between these things are the building blocks of semiotic meaning and changing them after the fact is not improving user experience.