honestly, the landscape is way more scattered than you'd think. Archive of Our Own obviously has the biggest volume, but the quality's a total mixed bag. The tagging system is both a blessing and a curse—you can find a 'Scott Pilgrim x Scott Pilgrim vs. The World: The Game' tag next to a 'Kim Pine x Kim Possible' tag, which sounds wild, but execution is everything.
Some of the most interesting takes I've seen actually pop up on smaller, fandom-specific forums. There was this one ongoing serial on a now-defunct indie comics forum that crossed the 'Scott Pilgrim' universe with the vibe and characters from 'Seconds', Bryan Lee O'Malley's other book. It treated Kim with this incredible, grounded weariness that the movie version hinted at but the comics really fleshed out. It got abandoned, though, which is a tragedy.
The real trick is filtering for authors who understand Kim's specific brand of cynical, bass-playing realism. Crossovers that just plop her into another 'quirky' universe as the sarcastic friend miss the point completely. The best ones force a clash of worldviews—like, I remember a one-shot where Kim from the comics ends up in the mundane but brutal world of 'The Sopranos', of all things, and her deadpan assessment of the mob drama was weirdly perfect. You don't find that on the big archives; it was linked in a Discord server dedicated to musician characters in fiction.