To know if someone blocked you on Instagram, you can look for several signs:

• Search for their username in Instagram. If you cannot find their profile through your account but it appears when searched from another account or while logged out, you are likely blocked.
• Visit their profile from your direct messages by tapping their username. If their profile shows no posts despite having posted before, and you cannot follow or see their content, you may have been blocked.
• If you try to tag or mention them in a post and Instagram prevents it, this can indicate a block.
• When you open an old DM conversation and tap their profile, if you see “Instagram user” with no profile picture and cannot view posts, it likely means you are blocked.
• Trying to open their profile link in a browser while logged out: if the profile is visible but not when logged in, it confirms a block.
• If the follow button on their profile switches back to "Follow" after you press it, you have been blocked.

These methods help differentiate between being blocked and account deactivation or username changes. If their profile is simply private, you will see a message to send a follow request but can still find the account in search. In summary, inability to find, view posts, follow, or interact with a user's account while others can do so usually means you are blocked on Instagram.