This can happen; if you're found unconscious and taken to the hospital, you can be billed for medical care which you didn't ask for, based on the doctrine of presumed consent.

One could imagine a parallel -- a critical emergency where it's impossible to communicate but it's reasonable to presume that they would want to have the issue fixed if they were aware. I don't think it necessarily applies here, but it's at least possible that another case could meet that bar.

I mean, why should I even need to apply for any job? McDonald’s always needs workers; do you think they’ll mind if I walk into the kitchen, start flipping burgers, and then name my hourly rate at the end of the day?

In this case there was a bug bounty program, so it is not as unsolicited as someone washing your windshield at a stoplight.

Secondly this is not a personal residence, thirdly the property was never broken into by the researcher (nor locks changed), finally there's is fiduciary duty from the company to their clients/users.

Since you are keen on hypothetical scenarios, let me present to you a more similar scenario. A school is situated near an old tree in a nearby lot that has a risk of falling, either on the school or on the public sidewalk, the researcher notices it, rents the nearby lot and safely chops down the tree. Then sends a bill to the school for chopping down the tree.

It is important to note that I didn't ask the question in order to get the opinion of strangers on what should happen based on personal ethics, rather I asked the question in case someone knowledgeable about the law knew the actual answer as to what the courts rule.