This is a common mistake that and it’s dumb that none of the UIs (or apparently any of the apps) make clear, but a post can only have an image or a link as it’s main thing and image takes priority, losing the link.

You can do whatever you want in the body text, having multiple images and links etc, but only one or the other for the “main post item”.

OP needs to just put the link in the body text.