u/Dependent_Coffee_701

I've been doing these on my sudoku app for a while and there's 5 difficulties. I never looked up specific strategies and have been just thinking about it logically, learning that way. I was doing the 4th difficulty, expert, but eventually I felt it was too easy. Since I got started on the most difficult, extreme, I often run into a wall. Due to this, I've been researching various strategies but I haven't found any that are relevant to this puzzle.

Can anybody help guide me in the right direction?