Currently, a form can only have one file uploaded per submit, unless the upload button is placed on the form multiple times. This seems it would only work well for a predetermined number of files to be uploaded.
For a client-facing website that may need anywhere from 0 to 10 (or more) files uploaded, it would be super helpful to have a way to upload multiple files with one button – to multi-select the files for upload. In case it's helpful, there's a super simple example here: https://www.w3schools.com/tags/att_input_multiple.asp
Perhaps another simple way to provide that, would be to add a drag & drop file upload, similar to that found in WordPress Media Upload.
I'm not a developer, but here are some other resources I found that might be helpful: