You were able to post the screenshot, because it's a smaller file than your pictures. You should be able to edit a picture and save it at a smaller resolution, then try uploading it.
I’ve had the same problem since getting a new phone. Only way I can post is to screenshot the pic (on my phone), then upload that. Complete pain in the arse.
Yeah. That’s my problem too— a new phone and uploading photos has become almost impossible with it to this forum. I tried resizing and sometimes that doesn’t even work but I kept shrinking them further and finally got it to work.
You might be able to get into your camera settings and pick a file type. A choice for jpeg might yield small enough file size without having to loss the data further.