It's true that many cars have been adapted with a protective panel, and that most no longer accept front-seat passengers, but it's still necessary for people to wear a mask at all times, and Uber wants to make sure of that.
The company will soon require users who show indifference or ignorance of the basic rules to undergo additional verification. If a driver reports that a passenger did not have any protective gear, that person will have to take a selfie with a mask or face shield before being able to make another trip with Uber.
In other words, Uber will not ask everyone for a selfie, only those who were reported by the previous driver. Of course, this may be subject to change if cities clamp down further on mask requirements.
This is one more step taken on May 13 in response to the coronavirus pandemic. He already requires his drivers and delivery drivers to wear a selfie with a mask, and he already asked passengers if they were following the rules, but now they are expanding the safety checklist to prevent users who repeatedly violate mask policies from using the service.