I studied art up to A-level in school, but the syllabus at my school and sixth form (UK early 00s) were so focused on how to become a modern fine artist (ie. how to document your process and develop pieces for exhibition focused on the meaning and novelty of the work and the exploration that went into it over the actual quality of the piece) rather than grounding in the basic principles of art like anatomy, perspective, value, composition etc. I largely consider myself self-taught.
I read a lot of books, practiced, made webcomics and got feedback from peers and industry professionals through uni even though what I was studying in Uni was English Literature and Japanese. When I finished university, I found myself more in demand as an illustrator than a Japanese-speaker, so I just kept going, then saved up and went back to Uni to do an MA in Games Design. There was an artistic component to that degree, but the only tuition was in 3D modelling since I was already a professional-level illustrator (that's how I got onto an MA unrelated to my BA).
Honestly only a minority of pro Illustrators I know have relevent academic qualifications. Most of them just took their hobby very seriously and got really good at it.
Art school does sound good for exploration and also for making contacts and learning how to market yourself and manage projects though, those are definitely some things I missed out on and see in friends who did go.