The difference between so much and so many is the same as the difference between much and many. So much is used with singular uncountable nouns. So many is used with plural nouns.

I have never drunk so much wine in my life. (NOT I have never drunk so many wine in my life.)
She had so many problems that she didn’t know what to do. (NOT She had so much problems …)

Note that before adjectives and adverbs we use so, not so much.

She is so beautiful. (NOT She is so much beautiful.)
You are so kind. (NOT You are so much kind.)

But so much is used before adjectives and adverbs in the comparative degree.

You are so much more beautiful now. (NOT You are so more beautiful now.)

So much and so many can be used without a noun if the meaning is clear.

‘Would you like some more meat?’ ‘No, thanks. I have already eaten so much.’

Special structures with so much

We can use not so much…as or not so much…but to make corrections and clarifications.

It is not so much his looks that I like as his personality.
It is not so much that I don’t want to come, but I simply haven’t got the time.