If the user has blocked your main account, you might be tempted to create a fake account. This violates Facebook’s Terms of Service and can result in all your accounts being permanently banned. Not recommended.
So if you see a website claiming "Facebook official locked profile viewer," that is a lie. Facebook has no such tool.
We’ve all been there. You get a friend request from someone, or you look up an old classmate, only to find that their Facebook profile is locked up tighter than Fort Knox. You can’t see their photos, their friends list, or their posts.