There have been multiple reports from Galaxy S20 Ultra owners of their phones developing cracks on the huge camera glass. Some claim it happens even without dropping the phone or any such impact. While the veracity of such claims remains in doubt, Nillkin is already selling a case for the S20 series that offers a dedicated slider for the camera glass.
https://www.notebookcheck.net/Galaxy-S20-Ultra-Nillkin-s-Camshield-Pro-Cover-case-offers-protection-for-the-delicate-camera-glass.465348.0.html
It makes sense whichever case. Keeping smudges from the cover glass is also a merit.