There are a few specific fields / settings in GravityForms that are not accessible, but they do a good job of warning, in form, when they are not. See https://docs.gravityforms.com/field-accessibility-warning/ , for specific examples, such as multi-select, and enhanced user interface for dropdowns (filter and search).

The only (minor) thing I'd say is that GravityWiz's Advanced Select perk has shown that it IS possible to make the enhanced user interface accessible, so I wish that could be implimented in Gravity Forms core as well.

Overall, I've been extremely impressed by how Gravity Forms does out of the box with accessibility.