I don’t know about hard cap but I have never managed to upload a file over 20-30mb - the upload would keep failing. I would think 1-200kb would be fine though.
For uploading large files you can use www.adalify.com which integrates a different file uploader into your app.
The maximum file size for both image upload and file upload is a hard cap at 50mb. Anything above this will prompt the user that the file is too large.
It’s also important to give the device time to upload the file before navigating away from that screen.