There are a few reasons why you might be seeing the message user not found instagram.
1. The account you are trying to view has been deleted or deactivated.
2. The user may have changed their username, so the previous URL you were using to access their profile is no longer valid.
3. User has blocked you, preventing you from seeing their profile.
4. It could simply be a temporary glitch or technical issue on the Instagram platform.
If you continue to see this message, try refreshing the page or logging out and back in again.

For more read - https://cursedmetal.com/blogs/73527/What-Does-it-Mean-if-a-User-Isn-t-Found