Pixels have never had a lot of different modes, because the computational photography is so good at making your images look as close as possible to real life, without excessive color saturation. You can always apply filters afterwards, if you want the photo to look a certain way.
The main mode that the camera will shift to is Night Sight, if it detects the ambient light isn't enough for a good regular shot. But it can also tell if you're trying to do Astrophotography (which typically requires the phone to be stock still, i.e. on a tripod).
I may be wrong, but I think 3rd party camera apps can't take advantage of the Pixel software.