Its hard to keep track, but so far...
Its 8 books (potentially up to 12 and more by 2022 and beyond when they enter phase 2) which will be released under Disney-Lucasfilm Press, Del Rey and Abrams Books, plus 3 short stories which you can only read via separate Magazine releases, two separate comic runs by Marvel and IDW, a Disney+ show, a supposed animated show (might be the Disney+ show), two other unknown projects, and one Chinese-exclusive story which takes place at the end of the High Republic with no intention of releasing it outside of China. And its all necessary to follow the plot and know how it ends, which is why they started the 420 Republic web show starring that twitter BLM warrior to "keep fans informed and let them know what's going on".
For comparison, the New Jedi Order project was limited to one book series under a single publisher with only a Dark Horse comic run that served as a side story that could be read independently from the novels. And with Shadows of the Empire it was only one game, one novel and one comic run, where you didn't really need all of them (considering they were mostly adaptations of the same story with some bonus content) to get the whole story. Disney did the same thing they're doing with High Republic with the "Journey to" shit used for the sequels. Only pre-Disney multimedia project that come close to High Republic in sheer content are the bloated Attack of the Clones tie-ins (and Filoni Wars shit if we don't count it separately) but those were at least tie-ins for a major motion picture, not tie-ins for a tie-in to something that doesn't even exist just for the sake of having tie-ins to make up for the fact that their attempted efforts at making a new trilogy after their horrid sequels backfired blew up in their faces after JJ and Rian kept fanning the flames and Game of Thrones' D&D jumped ship from their trilogy project after realizing that Disney put them on a sinking dumpster fire.