Changing your Default Preference to Private

• From the Settings page, click on the 'Privacy Controls' tab on the left side.
• Select 'Only You' under 'Activities.'
• Your default “Activities” privacy control will ensure that all future uploads reflect your selected preference. This setting does not retroactively change the privacy control on past activities.

OR

• Adjusting Individual Activities to Private
  • The individual activity privacy controls are also available on the upload page on mobile and web.
  • On the web, go to the activity and select 'Edit' (pencil icon.) Select 'Privacy Controls' to 'Only You'.
  • On the mobile app, go to the activity and select 'Edit.' Change your settings under 'Visibility' to ‘Only You' .

You’ll know that your activities are private when there is a locked symbol 🔒against your activities (see screenshot)

Answers copied from 😎 - https://support.strava.com/hc/en-us/articles/216919377-Activity-Privacy-Controls#:~:text=From%20the%20Settings%20page%2C%20click,uploads%20reflect%20your%20selected%20preference.

Thank you to those who participated and congratulations to @gf71_2 , the winner of this round of Wisdom Wednesday!

To learn more about activity privacy, check out these support articles:

Activity Privacy Controls 

Strava’s Privacy Controls FAQ

Activity Privacy Considerations 

Group Activities Privacy Controls

Your Privacy Defaults When You Create a Strava Account

Thanks so much @Kimberly22