I recently got a Samsung watch 5, but I've not been able to switch between the back and selfie camera on the camera controller app. I can only switch the cameras on my phone. I've tried different gestures, swiped up and down, flicked the screen.
Currently, you can only switch between photo and video mode and zoom in/out. Switching between back and front cameras is not possible.
May be it will be made available in one of the future updates. I had raised this with Support last year...
A bit about the current functionality here,there are limitations which many Smartwatch users will be aware of. https://www.androidcentral.com/wearables/how-to-control-galaxy-phone-camera-with-galaxy-watch
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My Device- S21 Ultra 5G ( SM-998B/DS ) CSC= BTU , 12GB/256GB
One Ui 5.0,Android 13 .