Sorry about the joke understandable only for French academics. The Sorbonne as a single university ceased to exist circa 1970 and was subdivided into several universities, some of which kept "Sorbonne" in the name for the aura. Futhermore, in the 201x and later years, there have been mergers.
So today "Sorbonne" can mean
Sorbonne University
Paris 1 Panthéon-Sorbonne University,
Sorbonne Nouvelle University
It's also the name of a big building in which all these universities have some space.
At some point, Université Paris XIII, which is located in a northern suburb away from Paris, was called "Sorbonne Paris Nord".
Some French academics joke that since the Sorbonne is the only French university known by foreigners (even though it no longer exists), we should rename all universities accordingly (Université Sorbonne Alpes, Université Sorbonne Côte d'Azur).