[In Omnibus]

The problem isn't going to be resolved by changing the forum software. People who expect social media functionality from forum software are barking up the wrong tree. They serve two entirely different purposes. Forums were never intended to be (and still are not intended to be) repositories for large images. Images are getting larger and higher resolution with every new device but PHP limits are still what they are, which is generally considerably smaller than images from modern mobile devices. Image SEO has always been a major pain in the ass and nothing has changed about that. Images themselves do not usually include captions or descriptions or meta data that tells browsers what they are. That all has to be added by the uploader or by the site hosting the image. It takes far more time and effort than most people are willing to give it. Again, changing software isn't going to fix that.

There are probably good reasons for moving to a more modern software, including SQL and PHP compatibility but it's doubtful that change will resolve your primary issues and concerns on any meaningful level.