Is it possible to view the screen on a RC in 16:9 and take a photo in 4:3 simultaneously?

Hi there. Thank you for bringing this query to us. When shooting vertically using the DJI Mini 3, it is normal that the live feed or the camera view on the remote controller will also turn vertical or in portrait mode. We will take this as a suggestion of yours and will forward it to our designated team for attention. Thank you for your valued support.

Not sure if we are talking about the same thing here...

No sadly you can do that,  You'd need to switch to video mode to see in 16:9