Yes! You can record, create, and release a track that is a cover of an existing song (for example: you want to create a cover of the song "Blinding Lights" by The Weeknd.)
However, the cover song that you create must remain fundamentally unchanged from the original. This means that the main elements of the original song, such as the lyrics, song title, and melody, CANNOT be changed. If those elements are changed, your track will not be considered a cover song anymore, and is not allowed.
To mark your song as a cover on the Starmony app, simply press the "Cover version" field while you are in the release flow, click "Yes", and then "Save".