Using the 2A Plus and Beta 3.0 you can not set the Nothing Gallery as default even if you disable Google Photos. After you take a picture and click on the photo you took in the camera app, nothing happens it will not load. So I think only the stable release allows you to set Nothing Gallery as default. So 2A Plus users will have to wait until next month to set as default when the stable is finally released on the 2A Plus.
