If your work is tracked in an issue-tracking system, you can put your in-progress thinking notes as comments there (if they don't go in the code or some other artifact).

It helps to have a safe environment, among whomever might access that issue comment history. If people don't feel safe exposing their thought process, then they won't do it, or they'll be stressed by presenting vulnerability, and even modify their problem-solving for appearances.

(I have some more complicated options involving a wiki, but explaining requires too much context. The issue-tracking comments solution is obvious.)

What I try not to do is to introduce new places that important information goes. If you don't rein this in, there will be an explosion of employees plastering your IP all over a bunch of random SaaSes, to be undiscovered or even lost to your company entirely (also, those other SaaS companies and hackers might get more use out of stealing your IP than you do).