I would like to be able to select multiple attachments when adding them to the attachment control. I believe that this is not yet possible (i.e. you can add only one attachment at a time when you click the "Attach file" button).
I would also like this functionality. I was a bit surprised to not be able to select multiple attachments in the open file dialog box.
Currently we are attaching photos to Sharepoint List. I would use the camera control directly but we are also limited to 640x480.
Since we are also using a Win 10 Tablet we don't get the option to take photo. We have to take the photos outside the app and then attach them one at a time.
From what I can see this is only possible if you use modern experience default form.
Otherwise, it's a pain being able to only select one attachment at a time.