Your Circles are never revealed to other Google+ users, but your friends are by default. Fortunately, there s a way to limit who can view your Google+ friends and followers. In the Privacy tab, under Sharing, click Edit network visibility. Simply uncheck the two boxes to hide (or selectively hide) who you ve added to circles and conversely, those who have added you to their circles and keep your friends to yourself. 2019 was a tumultuous year for Facebook as it continued to grapple with privacy fallout after Cambridge Analytica.
Source: https://threatpost.com/hell-is-other-people-network-visibility-on-g/91842/