Hi @StephanFink
Welcome to Connect.
Let me try to understand your issue.
Are you able to upload photos to a review?
In English the term Caption is often used for Subtitles. A new form of captions was introduced a few months back, but I trust you mean the old captions belonging to a photo as seen below:
This screenshot is from my android phone. The arrow shows the icon used to type in a caption.
I will check on my Iphone and comeback should I find a way to add such captions from there.
Cheers
Morten