De nauseam :) this is one of the basic Qs that plagues Korean learners and has been answered hundreds of times if you do a little search.

First,  you have to split it into its components.  Then learn the difference between those components.

나는, 저는, 내가, 제가...these are nouns combined with particles.  It's like "an apple" and "the orange". You're trying to look at the difference for two different things at once (a vs the, apple vs orange). What you have to understand is 나 vs 저 and 은/는 vs 이/가.

나 and 저 both mean "I, me". 나 is informal (friends,  family, younger people). 저 is humble (and therefore more formal) (strangers,  older people,  bosses....). 은/는 vs 이/가 is the real issue.  The difference is not clear to almost any Korean learner. It's generally more subtle/nuanced but can definitely change the meaning. There are some general rules of thumb but no clear rules/ Explanation. It has been explained thousands of times so I suggest looking it up and finding the explanation you understand best.

Therefore 나는 is the informal form of 저는 (but same in meaning).

Therefore 내가 is the informal form of 제가 (but same in meaning).

Therefore 나는 is the same formality (informal) as 내가 (but different in meaning).

Therefore 저는 is the same formality (humble/formal) as 제가 (but different in meaning).