Can I send a session to my watch?

Yes, with Send to watch on a planned session, on the Agenda and on Now. It goes through Intervals.icu, which passes it on to the watch you have linked there, or to an Apple Watch through the Trailwise app on your iPhone (iOS 17 and watchOS 10 or later). Each session shows whether it was sent. If a session cannot be expressed on your watch, Trailwise says why instead of sending it.