I'm not sure there's necessarily a big difference between the way people post publicly visible content and non-publicly-visible content.

Posting a comment on reddit vs posting a comment on Facebook.

Posting a meme on reddit vs posting a meme on Facebook.

Posting a comment on a public Facebook post vs posting a comment on a private Facebook post.

Posting a post in a public Facebook group vs posting a post in a private Facebook group.

Posting a comment on a YouTube video vs posting a comment on a Friend's share of a Facebook video.

Posting a comment on a public Facebook video vs posting a comment on a friend's private reshare of that same Facebook video.

Posting a picture on reddit vs posting a picture on Facebook.

Posting a picture to a public Instagram profile vs posting a picture to a private Instagram profile.

Posting a picture to Twitter where Twitter tries to make everyone log in before viewing the picture.

Sending money with some message on Venmo back when all transactions and messages were public by default (up to last year).