Active learning is characterised by producing something and then comparing / critiquing it against a well-known production. Often STEM subjects fit this very well because they are almost entirely built on the premise that you make predictions with a model, perform a test, and then refine your models.
Anything mathematics, logic puzzles, etc. would fit into this quite well since you don't really need specific equipment, you can attempt to solve something and after having a solution you can compare it to what a book / the internet says. Then critically evaluate how you approached the problem vs the actual solution, and the merits/demerits of each approach - as you grow you can probably find multiple competing solutions (being able to discern between them is very powerful)
Personally I really like programming because of the immediate feedback loop, needing to hold a program in your head, reason with and refine that mental model of the program. Also with programming its easy to work on something a bit more interesting: games, websites, dbs, etc.
I think you can also look into essay writing or other fields but its extremely important to have someone to spar with - otherwise you don't know if your thought process has actually improved.