Facebook: Friends are always mutual, and require a request. You can choose which posts are publicly available, and which are for friends.
Twitter: All posts are public, unless you have set your account to private, and then followers will need to request.
Mastodon: Private or public accounts. Every post has one of four privacy levels, which can't be changed later, and there is a multidimensional matrix that describes what posts can be seen by what users from where at what time.

@impiaaa I thought this was a joke post