how do I enable autosave activity

To my knowledge that is not possible (even on a 965) . You have to select one of the options on the screen after stopping,

The user manual says: " After stopping the activity, the watch saves it automatically after 30 minutes."

I don't think there's a way configure this time period though. It was actually an annoyance for me on a Venu 2 that didn't have resume later when it would save an activity while paused at e.g. a coffee shop.

Great. Thanks! I will just stop the run and let it autosave next time.
Here is the reference from the user manual in case others want to see more detail:
www8.garmin.com/.../GUID-7D2E0DD7-438F-4362-948F-000FCD0AF4D2-5144.html

Interesting thanks, I just save immediately , waiting 30 mins seems a waste of battery and my time! good to know if one forgets to save though i guess.