Instagram does not have one algorithm, it ranks each surface differently. Feed and Reels reward watch time, saves, shares and comments, not raw follower count. It shows your content to a test group first, then widens if they engage. Make content worth saving and sharing and post in one clear niche so it knows who to serve you to.
What the algorithm rewards
Each surface ranks differently but engagement drives all of them.
Saves and shares over likes
A save or a send is worth far more than a like.
Watch time on Reels
Short Reels people finish get pushed the widest.
Consistency and niche
A clear topic helps it find your right audience.