Commercial Social Networks are accessed either through their own app, or a web page. In either case they exist as an island, although a giant one, accessible only to its inhabitants. If you want to visit these, beyond a teaser glimpse, you have to create an account, allowing them to claim large population and influence, and data to sell to the advertisers who fund them.
There are also a large number of much smaller islands, which welcome visitors. You do not need to provide any form of identification – such as creating an account to look around, though you will need an account somewhere on this network of sovereign areas to follow or comment.
Examples
Here are a random selection
https://mastodonapp.uk/@uktw – UK Theatre Web
https://mastodon.social/@gutenberg_org – Project Gutenberg – if you are into books, so are they.
https://mastodon.scot/@scotlit – Association for Scottish Literature – -if you are into Scottish Books
https://mastodon.social/@onlmaps – interesting maps
https://mastodon.social/@medieval_illuminations – Medieval Illumination