Instagram doesn't send out a notification to tell you that a user blocked you
You will never know unless you investigate
Here are some ways to know who among your followers has blocked you
Search for their account: If it doesn’t open up then you have been blocked
Use an old comment or a DM: If it shows no posts yet on top then you have been blocked
Visit their Instagram profile on the web: If you can see profile on browser but not app then you have been blocked
Try Following Them: If the blue follow button is not working then you have been blocked
If the user has liked and commented on videos but can’t be seen on app then you have been blocked