On places like Facebook if you have sorted your friends and acquaintances into categories you can post to any or all of those, or you can post publicly so the whole world can see. I don't think there is such a breakdown in Instagram. On Twitter you can (could? I haven't looked at it for a while) categorize the accounts you followed in lists then go to each list to see what was current. I don't know if you could make X posts anything other than public (the whole world) or private (only accounts you allow to see your content.) The rest of it - I don't fool much with TikTok, never look at other venues.