First of all, he may be proud of his figure and fitness achievements, hoping to show his efforts and achievements by taking pictures.
Secondly, he may want to attract people's attention by taking pictures, hoping to get more attention and recognition. This behavior may imply that he is eager to "decorate himself" or feel inferior or unsafe.
Finally, he may not realize the importance of personal information protection and privacy, and ignore the protection of his personal information on social media.
If you are not satisfied with his behavior of showing fitness achievements in the circle of friends, you can communicate your thoughts frankly with him, tell him your feelings and respect his rights and needs as an individual. Mutual communication and understanding can strengthen mutual feelings and increase trust and understanding.