The process will usually go away itself when its job is done. This causes some Windows 10 PC especially laptop/notebook computers to go very loud and high in temperature when this process runs during idle which your PC is supposed to be silence and cool. In order to find these newly downloaded or existing photos and videos files and to create shortcuts for them in the Photos app, the process will have to run on high CPU and memory usage in the background to be able to do that. Open Photos app now and you can see a list of photos and videos you recently saved in your computer.

This is to allow you to have access to all your media files at a glance.

The would also run in the background to search for all photos and videos available on all of your disks and to create shortcuts and thumbnails on the Photos apps. To generate these thumbnails, it is set to run in the background only when your computer is idle so that it doesn’t interrupt you when you use your PC. This will allow File Explorer to quickly show you folders with thumbnail without much loading. The process also handles jobs such as generating and creating thumbnails for your folders that have photos in it.

Why does it also appear when Photos app is not open?

Microsoft photos .exe