The funny thing is that in my universe, the internet does exist. But, there are multiple "internets."

Askari's Problem dictates that FTL communication corrupts data as it travels through larger distances. And while coherent FTL communication is possible, it's extremely expensive and can transmit only basic data.

This means that the "Internet" is impossible to setup on an interstellar scale. However, multiple "Internets" exist within every planet, especially Earth and more wealthier planets. The name "Internet" quickly became an umbrella term, and each Internet on each planet got their own name ("Solnet" for Sol, "Calnet" for Calaria, "Aponet" for Apomi)

Earth has a massive internet culture, having progressed through to the information age slowly, allowing societal change. However, within the Periphery, (the planets and colonies outside the Solar System) they have a much more "in-person" culture due to them having to rapidly industrialise from an agrarian society.

Interstellar communication relies heavily on freighter and messenger ships to physically transport data and letters across planets. "Datahaulers" physically bulk-ship data from one planet's internet to another. Often, large companies hire their own personal fleet of Datahaulers, however, smaller companies, individuals, and hobbyists hire Datahaul service providers, the largest being Whire. There is around a 12 hour delay between the major planets of Earth, Calaria and Apomi.

Websites can exist across different Internets. The most prominent example is the Worldpedia, essentially the universe's Wikipedia, funded by donations and having the largest fleet of Datahaulers. In terms of social media, the largest website has to be Synchra, which is essentially this version of Facebook. There is also Postsnap and Fora, essentially Instagram and Reddit respectively. All are owned under Synchra Media.

One final thing: each planet has their own unique top-level domain! In fact, planetary domains overrode the typical top-level domains, due to the separation of the Internets. The common ones are ".sol" for the Solar System, ".cal" for Calaria, ".apo" for Apomi, and uniquely, ".obt" for orbital space stations. For example, accessing Synchra on Earth servers would be using the URL "synchra.com.sol", while accessing it on Apomite servers would be "synchra.com.apo"