[Help] I'm good at leetcode, bad at Big O

I can solve most leetcode mediums no problem with the optimal solution. The problem is after I try to write the time complexity, and if it isn't O(n) or O(n^2) I pretty much get it wrong 100% of the time. I'm a bit close but never right.

I tried quizzing myself with chatGPT but still I just get it wrong every time and after doing this 3 days I'm not better.

Why do I suck so bad at determining big O and any tips / how do I get good at it?