What book would you recommend to significantly improve my problem solving skills?

The ruling class doesn't want critical thinkers.
It wants trained workers.
Apparently you've outstripped your school's ability to educate you. So move on from the Dummy Down Dunce Dance school you're currently attending. Learn math on your own.
Choose the topics that most interest you and study them. That is where you'll excel. Skip that I've got to curriculum, it's just baggage. If you bump into something that you like but lack the background, then you'll be motivated to study the background material.
Skip that high school stuff and look for a community college that'll accept you. You'll likely be happier there. Visit a community college, meet with a math teacher, and find what opportunities be there for you. I have a friend who got so bored with high school, she attended a community college instead where she was happier. I also know a self tutored math student who was accepted into a liberal arts college based upon his success in a college math exam.
PS. Skip the most modern text books and look for books written for mathematicians where the cook book method is ignored in preference to concepts, theorems and proofs.
Good luck with your struggle living in a country where being of above average intelligence is a handicap and with your new adventure beyond high school into adult education.
PSS. If you want a tutor, I'll give you a throwaway email address by which you can contact me. I have successful experience tutoring both elbow to elbow and by phone. Being retired, I've no need of payment.
I also suggest you use this web cite for questions and when you get stuck understanding a concept or a formula.

Yes, I think the Art of Problem Solving is a good book series.

I have not heard of Solving Mathematical Problems by Tao, though, but I do know that you can practice your mathematics skills by completing AMC Tests from past years here.

https://artofproblemsolving.com/wiki/index.php/AMC_Problems_and_Solutions