Instagram carousels can have up to 10 slides (photos or videos).
Due to restrictions from Instagram's API, you are limited to 10 photos / videos on an Instagram carousel post.
Tips for carousels with lots of content
If you have more than 10 images to share:
Combine images: Combine multiple images into a single photo
Split into multiple posts: Create a series of carousel posts
Prioritize: Choose the 10 most impactful images for your carousel