When I hire people, aside from fixing mistakes in the documentation they encounter, I want them to have all the time they need to learn, ideally with a set of curated onboarding tasks that progressively give them expertise in the system they are intended to operate in. There is a time to "make things better" and, in my opinion, that's after getting up to speed in a sense that lets me collaborate with the team in a productive manner. I won't begrudge someone the opportunity to clean things up, but each individual is the ultimate arbiter of how to be effective at the end of the day.
I’ve never onboarded to a team that had such an experience, I’ve never heard of a team with something like it consistently, every time I’ve seen it proposed and tried it takes time away from an experienced person (who could have done those same tasks faster) and goes out of date as soon as one new teammate completed the curated set of tasks.
If you can make it durable, my utmost respect!
In the meanwhile, deleting obviously dead code has never failed me as a strategy for myself or a new hire (typically steered by a simple oncall-type task to start the investigation off).
And best part, there is always more to clean up for the next new hire lol.
If you have a curated onboarding experience that's great, but then you'll probably have good documentation and nice setups, then my suggestion obviously doesn't apply. I wish that was common but in my experience that has been a rarity, not the common case.