This feature is work in progress for v3.5, you can try it downloading and installing the last development build from
https://github.com/GoldenCheetah/GoldenCheetah/tree/v3.5-DEV1708
The Share > Add Cloud Account... wizard allows to authorize your Strava account and enables a new menu Share > Synchronize Activities > Strava
Bidirectional synchronization is working but there still some known limitations:
- On Download gaps in recording s.t. generated by Garmin Smart Recording are not automatically filled, this can be fixed using Edit > Fix Gap tool, but Laps get out of synch and pool swims are not imported correctly yet.
- On Upload laps are not synchronized and you cannot restrict which data series to upload.