If you're a power user of the Microsoft Photos app on Windows 10, you're in for a treat. Noted by MSPoweruser, Microsoft recently updated the app with a new favorites feature, bring it up to version 2018.18051.18420.
To find the favorites feature, simply open up the photo you'd like to favorite and then press on the heart-shaped icon on the top middle part of the screen. This will mark your photo as a favorite, and put it in a dedicated favorites folder.
According to some reports, this feature is tied to a server-side update, so you might not be seeing it at first and possibly need to wait for it to appear. Also, please be aware that photos marked as favorites will not sync between devices, and you can't mark down OneDrive photos as favorites.
At any rate, feel free to update now via the link below. Once you've grabbed this latest version, let us know in the comments below how you're finding this new favorites feature.