Sorry, the Android 11 Device is my mother's phone, and she was using it, so I couldn't test using it.
Right now, upon testing with the Android 11 Phone, I still wasn't able to figure out how exactly do I solve my problem.
I even tried giving the full file path (/storage/emulated/0/Android/data/edu.mit.appinventor.aicompanion3/files/Pictures/app_inventor_1619777203718.jpg) as an attachment, but it still isn't working.
Even If I use that extension, how exactly do I make it work?