While it's great to have a quick upload to Vimeo (System Preferences app → Extensions → Share Menu) in Photos.app, what about a share extension to quickly upload videos from Photos to YouTube? Does such an extension exist that can be added to macOS?
While such an extension doesn't exist natively in macOS, the desired functionality can be added with the support of a 3rd party app.
Video Uploader for YouTube is a macOS app which lets you easily upload your videos to YouTube.
The app also installs a Finder and Photos.app extension which lets you upload to YouTube directly from Finder or from within the Photos app.