@RF

You've got to do it in the standard reply, not the quick reply.

Stepping thru this on my phone, should be same on computer.

Can't see button for Reply. I clicked Quote. Took me to page with options.

You can delete qoted text.

Click on paperclip icon, not the photo icon.

Click upload new file.

Click add files.

Click start uploads.

There's a red warning to wait, but should insert quickly.

Hopefully that helps. Or did you try that already...!