Is there really a way to see who viewed your Facebook profile? Keep seeing apps that promise it.

No, and this one matters. Facebook does not let anyone see who viewed their profile, full stop. There's no hidden setting, and every app, extension or 'trick' promising it is a scam that exists to steal your login, spam your friends, or harvest data. Facebook has said outright the feature doesn't exist. The only thing close is that Stories show who viewed a specific story, and that's it.

Total scam, every time. I fell for one years ago and it posted spam to all my friends. Facebook genuinely does not offer this and never has.

The Stories viewer list is the only real 'who saw this' on Facebook, and it's per-story, not per-profile. Everything else is a data grab, avoid.