32M How do I get to know my girlfriend’s needs better?

TL;DR we’ve been 8 years together but I still don’t know how to change her mood when she’s upset at me. How do I do it and how do I ask her in a considerate, thoughtful way?
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This might be a lot, so bare with me.

I’m 32. I have been with my girlfriend for over 8 years now, but in a lot of ways I don’t know a lot about her.

Yes, a lot of years have passed and we’ve done a lot together. But most of those years I feel I haven’t paid enough attention. It’s been a long time building up and I’m now facing the consequences.

Most of my life I have closed myself off from a lot of social settings like interacting with coworkers, or… I don’t have friends or places to frequent. This has built up to not knowing a lot about the world, about social situations, even about what my country’s people are like these days or how people my age behave and speak.

I have little to no experience with… anything. And because of that throughout the years I’ve been unable to give her nearly any advice other than what I “feel” about things. And have often found myself to be not confident and lost when we go out. Not everywhere all the time, but there’s a lot of “unexpected” situations where I’m not sure what to do.

The worst part of everything is that I have never known how to change her mood when she’s upset at me. And that stems from not knowing what she likes or dislikes.

I’ve tried flowers, letters, apologies(of course), giving space, bringing some snack or food she likes. But that can only go so far. In 8 years it becomes repetitive.

I sincerely, deeply love her more than anything. But I feel most of the time I’ve never been helpful in any way or truly known her.

How can I know her needs better and better understand her? How can I ask her in a creative, thoughtful, considerate way? What can I do to make her feel better?