Capcom has released the version 1.3.0 update for Monster Hunter XX Nintendo Switch Ver. in Japan, which adds the ability to record gameplay.
To record gameplay, press the “Capture Button” on the left Joy-Con (hold it until you hear a “pi” sound). This will allow you to capture up to 30 seconds of footage, which will be saved in your Album (accessible in the Switch Home Menu). From your Album, you can upload the footage to Facebook or Twitter.
Monster Hunter XX Nintendo Switch Ver. is available now for Switch in Japan. A western release has not been announced.