If you mean Flowers by Miley Cyrus, the chorus has long sung words (flowers, hours, sand, understand, dancing) which you can't do with film clips as it is highly unlikely to find someone saying those words stretched out. That's why I can't do any Mariah Carey songs as well, as she often sings one word as a long note varing the pitch.
If you mean Bad Guy by Billie Eilish, there is a lot of mumbled words near the beginning which I wouldn't be able to do. Also, a lot of the song is sung in harmonies which would be a single voice if using film clips and the main chorus is instrumental and would need clips of a synth playing or dancing. Not to mention I would need to find an instrumental version to use as a backing track and hope that it doesn't get flagged as a copyright strike and have the video banned. I did do a version of Girls Aloud cover of Jump a while ago and after a few weeks it got flagged and banned. It's uploaded to Vimeo at vimeo.com/746660907 and has been fine.
