Can people tell that I've seen their Facebook profile? ... No, Facebook doesn't tell people that you've seen their profile. Third- Who views your Facebook profile | Facebook Help Center

While the idea of a Facebook profile viewer might appeal to users' curiosity about their online presence, the lack of an official feature is largely due to the privacy and security implications. Third-party applications claiming to offer this functionality pose significant risks and are against Facebook's terms of service. As social media continues to evolve, finding a balance between user curiosity, privacy, and security will remain a critical challenge.

Facebook does not let you see a full list of who viewed your profile. You can only see people who actively interact with your posts or who view your Stories while they're live. Any app or extension that claims to show every profile visitor is misleading and may be harmful — avoid granting them access or sharing your login. Protect your account by tightening privacy settings, reviewing app permissions, and enabling two-factor authentication.

Facebook explicitly states they do not let people track who views their profile [ Third-Party Apps:

If you find an application on Facebook or a third-party site claiming to be a "profile viewer," you should report it to keep your account safe:

The screen went black.

let you track who views your profile. This is a core privacy feature designed to allow users to browse the platform freely without being tracked by others. The Danger: Third-Party Apps