I found a Hack to see the Reach of Hashtags on Instagram.
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Yes you can see the Top 5 hashtags of your post in your insights.
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This could be an old thing but I discovered it recently and thought of sharing since I never came through such thing.
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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! 😊