Multiple third party websites have integrations with Garmin Connect. You can therefore link your accounts and have your watersports activities uploaded to your favorite websites, completely automatically.
It is worth mentioning that Strava ignores Doppler speeds and only calculates speeds from the positional data. As such, speeds calculated by Strava should not be trusted, even for the Airoha-based watches. Strava can be thought of as a handy diary with a nice colorful map, but untrustworthy for speeds.