https://wccftech.com/google-photos-lets-you-share-photos-over-private-message/

Google Photos was already pretty good but it just got a whole lot better, as it now lets you share images over private messages. Until now, the only way to go about it was to create a shared album. There is, however, limit to the number of images you can share using this method. Don't worry about burning through it anytime soon, though, because it is set at 20,000 images.

Facebook Now Lets You Directly Transfer Photos and Videos to Google Photos