An exoplanet is a planet outsite the Solar System. There are more than 4500 confirmed exoplanets acording to NASA EXOPLANET ARCHIVE.
Di Stefano et al. have published a preprint article entitled "M51-ULS-1b: The First Candidate for a Planet in an External Galaxy" in september 2020, available Nat this website
The final title of the reviwed and published article is les optimistic "A possible planet candidate in an external galaxy detected through X-ray transit" avilable in nature astronomy