Apple - Are there iphone apps or automation for taking photos and sharing low resolution versions?

Did you look at Simple Resize which seems to do what you are looking for.

On iOS 12 - the app Shortcuts by Apple can automate all of this now for you.

• take a picture (preview or not)
• resize it
• save it to an album / share it to a shared album / save it to files (google / Dropbox / box / iCloud) / send it to an app

The last step can do just about anything you might want with images just taken and basically modify the camera to take reduced photos and optionally share them out as well if you don’t want to just have them taken.