for starters, I like the free articles on Upswing a lot. Loads of content on all sort of situations/game types for free, can’t go wrong with that.
Otherwise, there are also opening charts on them by position on the table, very usefull I’d say. Another kind of chart I like to review a lot is this one ( given I play turbo’s a lot online )
https://floattheturn.com/wp/pushfold/
you can also google things like ” how and what to 4 bet” and get an overview of the best free content.
that takes around 33% of my study/review time atm, the other 66% I look at my own hands I played, analyze them to see what I did wrong/could do better in the future and how this mistake ( or correct play ) can be prevented ( or perfectionised ) in the future