Not sure if it is possible for researchers to visit or if it is only for attorneys to find (or suppress) documentation for lawsuits. I know that research can be done in support of FAA questions.
Quote:
Boeing Archives arrives in new home, primed for the future
After months of careful planning, the place where company history lives is ready to preserve the next century of Boeing.
Nearly 25 million artifacts – and counting.
That’s how many pieces of the Boeing legacy now reside in the new home of the Boeing Archives in Auburn, Washington.
https://bit.ly/3AHeooA