Instead of treating your newness as a liability, view it as a superpower.
- Nobody wants to be mean to the new person, so you have the perfect excuse to request resources aggressively.
- You can observe problems with the codebase, processes, or tools that tenured employees have learned to tolerate.
- You can connect the dots between different teams or ideas that would be harder for people entrenched in their roles.
Approach your onboarding with the urgency that "You will never have fresh eyes again."
As the most clueless person, if you revamp a resource (wiki, code, etc) to be easy to understand for yourself, you are making it easy for everyone to understand.