See the first post here for a way to recalibrate the proximity sensor to avoid this issue. If it works you’ll not need the workaround with the power button anymore.
This issue is discussed here. Try the touch and hold delay workaround. Static could also cause this issue, so see if grounding yourself helps and if it does search for a reason for static (usually a faulty charging cable).
I believe it’s called google photos or just photos. I’m not using the standard OS with google, so I’m not sure. On FP Open OS it’s called Gallery. (Names may change with system language)