Just found this from another user in a different thread:
"Just also be mindful when using the P4P, that if you have the GO4 app in video mode and shooting video (or maybe even just in video mode - I've not tested), you can still take and save photos as jpegs , however they are not full resolution photos. They are basically a 'frame grab' from the 4K video feed. They are 8 megapixels and not the true 20 megapixel capture. They do look washed out and unsharp and reflect your video profile settings. You were not able to do this with the P3P, you had to stop the video record before you could take stills."
U can i did the other day while recording 4k video. U can take 8 mp stills. So yes it will work but its just a screen grab from recording not full resolution