Is iOS 14 compatible with Yosemite?

Mac OS X 10.10 (Yosemite) is required minimum for the new iCloud Drive and iOS 11 (except for Notes, which requires El Capitan). iTunes 12.7. 0.166 is needed for iOS 11. Also note, anyone who can install Mountain Lion can also install El Capitan, which supports all iOSes up to the iOS 14.