"San Junipero" is one of Black Mirror's only uplifting episodes, and is also one of its most popular. That's why it's not surprising to see a nod to it in scenes when Stefan goes to visit his psychiatrist, Dr. Haynes (Alice Lowe), who happens to work out of a medical practice called Saint Juniper's.
If you recall season four's "Black Museum" episode, there's a vignette that centres around a man's wife who gets hit by a van and ends up in a coma. The hospital where she's staying, which is also where other people are eventually duped into volunteering for dubious neurological experiments, is called Saint Juniper. This was likely ground zero for the development of the "Cloud" in "San Junipero," which we know was definitely created by the organisation TCKR in the Black Mirror universe.
In "Black Museum," museum proprietor Rolo Haynes describes Saint Juniper as "like" a university hospital, but never fills us in on who is at the top of the company (whether they're a government operation or private). Judging from this glimpse into the past, it seems the organisation has been around for quite some time.