For what it's worth, which isn't much because this is probably outdated: I remember trying grist a few years ago and leaving mildly unimpressed with form support (I think because I was hoping to have image upload in the forms and that wasn't supported yet).
Since it is relevant here: support for uploads was code written by a French contributor, and reviewed by a developer working for the French gov (ANCT/DINUM) and a developer working for Grist Labs. Grist Labs has since maintained and improved on it. The forms feature itself was inspired by an integration built by Camille Legeron at ANCT.
For what it's worth, which isn't much because this is probably outdated: I remember trying grist a few years ago and leaving mildly unimpressed with form support (I think because I was hoping to have image upload in the forms and that wasn't supported yet).