For the main camera there are cases with sliding covers for many phone models. Marketed for protecting the lens from scratches, but quite effective for privacy as well

For the front camera that's a lot more difficult. You could probably modify one of those flexible screen protectors to black out the camera, but it'd be very inconvenient to take off.

Maybe there is some niche android phone that offers physical shutters, similar to the ones on Lenovo laptop webcams