How does the NPC attitude work (how much they like or dislike you)?

Do NPCs dislike you for having demands on them, or for having made a demand on them?

Will they like you more if you withdraw demands, and does renouncing multiple grievances stack and make them like you more?

anyone?

Not sure about stacking and some of it depends on the personas biases as well. I usually look at the attitude arrows and try to figure out why/not they like me . A lot of things seem to factoring including what you mentioned. Active treaties, renouncing, their bias, grievances , etc

More examples from wiki:

• Actions such as buying Resources and making an Alliance can improve the relationships, while breaking treaties and pressing Demands can deteriorate the relationships.
• The differences in different empire ideologies are measured in Ideological Proximity, which can also influence AI Empire's Attitude.