I feel you on the challenges. I had the same culture shock going to high school, even though it was only a smallish Catholic school. Learning how to work within a system is a critical skill!
On math, my early elementary teacher and my father (also a teacher) combined Montessori math, which spoke to (or influenced) my visual/tangible style of thinking, and lots of classic drills to internalize math facts. Or maybe it worked out in contrast to your experience because something clicked and I loved learning math early. (High school beat that out of me.)
I feel pretty lucky that I finally found math that I enjoyed and made sense after hating it for so long. I didn’t do a ton of memorization/drilling and I never really got into the world of fun math puzzles, so in high school I was both underprepared and never got to do the cool stuff. It’s much easier to convince myself as an adult that fluency in algebraic computation is useful because I now have examples that I care about being able to work through.
On math, my early elementary teacher and my father (also a teacher) combined Montessori math, which spoke to (or influenced) my visual/tangible style of thinking, and lots of classic drills to internalize math facts. Or maybe it worked out in contrast to your experience because something clicked and I loved learning math early. (High school beat that out of me.)