I have literally been waiting for this question for 4309 years because now I get to talk about the best character in the world aka Terisa (of) Morgan (all of you go read The Mirror of Her Dreams, by Stephen R. Donaldson). Terisa is relevant to your question, I promise.
Mild spoilers for TMOHD ahead.
So Terisa is a mid-twentysomething who has a habit of fading. Not literally fading, but feeling like she is fading, like she doesn’t exist. No one looks at her directly, she has no friends and family (her dad is emotionally abusive and keeps his distance from her), she barely feels physical stimuli, and the only proof she has that she exists are the mirrors in her NYC apartment. She needs the mirrors so she can see herself and prove to her eyes that she exists. Because of her fading disorder, she is probably the most passive protagonist I have ever read.
Long story short, a guy (Geraden) crashes through one of Terisa’s mirrors and takes her, via mirror, to another world/dimension (Mordant) which is pseudo-medieval (and done really well). Mordant is on the brink of war. It has enemies on two sides, its king is insane (and several people are trying to replace him), and it’s being attacked from within by magic, which comes from the mirrors. (You make a mirror, it shows an image of another dimension/world, you open the mirror, and whatever is in the image comes out.) Geraden brought Terisa out of his mirror. He was supposed to bring a champion who would save Mordant. Most of Geraden’s fellow magicians think Terisa couldn’t possibly save a fly, let alone Mordant, but questions as to Terisa’s importance continue to make her a spectacle to important people in and out of Mordant.
Keep in mind Terisa’s in another dimension’s Middle Ages, knowing absolutely no one, with her fading proclivity. Her arrival in Mordant forced her out of her shell. People expect Terisa to know the politics of Mordant, so others present her with facts. She tries her best to string them together, for her own survival. She tries to make sense of her situation and her “sense" is toppled at least three times. She begins to connect with people in Mordant; when one of them is seriously injured while protecting her, she takes action. And she fails. People die. She contemplates fading but realizes more people will die if she doesn’t act again. Terisa has decided she must help people. She sidelines her “champion role” to focus on saving the people she likes. And that gives her motivation and drive to be an active character for the rest of the series.
tl;dr give your character a goal that they will chase with burning passion. A goal is your ticket out of passivity. If you can determine one or two things your character wants and let them chase it no matter the consequences, your protagonist will go from reactive to active.