I found a Hack to see the Reach of Hashtags on Instagram.
Yes you can see the Top 5 hashtags of your post in your insights.
This could be an old thing but I discovered it recently and thought of sharing since I never came through such thing.
Step 1 - Choose the post you want to see the reach of.
Step 2 - Click on Promote Post
Step 3 - After promotion Click on Insights
Step 4 - Scroll down and you will find top Hashtags and the number of reach
Your welcome! 😊