Instagram captions can be long or short. If you're posting a photo with a recipe, for example, your caption could include the entire recipe. The most important information in the caption must be placed at the top so that the caption can be read by others. However, if you're using Instagram captions to promote your product, you should keep them short. For a post on Instagram, you need to make it stand out.
See also - https://onlinegeeks.net/captions-for-profile-pictures/