Just over a month ago, this little kitten showed up on our doorstep. The security camera showed her making a beeline right up our driveway and onto the porch, where she sat screaming her head off until we heard and opened the door.
She was nothing but bones underneath the matted fluff, but she was immediately friendly and surprisingly trusting. I had been wanting a second cat and my husband jokes that my desire manifested this little one, who we named Sofrito, or Sofi for short. ♥️
From everything you've mentioned, it does kinda feel like she escaped and got lost. The b line for a stoop feels like she knew she came from a door that looked kinda like that. Hungry, matted, sick...for a full grown cat that's a good sign they're lost and not feral - feral cats usually have it worked out how to survive. With kittens it's either way, maybe she got separated from her litter instead, from her perspective that's the same kinda lost.
With that said, it sounds like you already tried a few things and I'm not here to say you should do more. Maybe a single flier outside your house just in case it's an immediate neighbor? Otherwise, I'd switch gears and be thinking how to protect yourself from a potential escape artist! Dress up your front porch (she keeps chewing a houseplant inside? Move it to the stoop. Work boots that smell like you? Store them on the stoop) and give her 10 minutes supervised time out on that stoop a few times while she's still a young kitten that you can corral. This way she recognizes the stoop if she's ever trying to find it AND also isn't immediately terrified if she darts out a door and finds herself outside.
Definitely also get that chip, but you already know! She's adorable!
She's gotten a little bit of supervised porch time, my husband and I plan on training her the same way we've trained our first cat, Mirepoix.
Mira loves her supervised outside time and understands when we ask "you wanna go outside?" She'll generally stay in the garden with us (occasionally she'll push her luck and wander a little) and knows when we say "inside!" that it's time to go in.