I have a Samsung Galaxy Watch Active 2, with all apps and the watch itself with the latest updates.
Yesterday I did a bike ride of approx. 14km, with a short hike afterwards (Approx. 1,8km). When I tried to save the hike the app said "Strava needs a longer activity to upload". I discarded the activity, and started a new bike ride. This bike ride was approx. 15km. When finishing this, the app gave me the same message. Today I did a new bike ride (Approx. 5,5km). This time I used both my phone and the watch. The watch gave me the same message, needs a longer activity to upload.