Our engineers like to take a lot of pictures using their tablet/phone photo app and then go to the field service app and upload all the relevant pictures in one go.

We use a PCF for the web browser app. However, that PCF does not work for the mobile app.

We discussed with the creator of the PCF and their feedback is that it is down to the mobile app, so it is up to Microsoft to allow the component to support multiple files upload or implement the batch upload feature directly. See https://github.com/ramarao9/AttachmentUploader/issues/27