When I was on the receiving side (there was a newcomer to the team doing a lot of "suggestions for improvement"), I made a lot of effort to explain the context that led to a different decision, but it was very draining and rarely the good time for it (it distracts from the conversation), it was really hurting collaboration. Eventually we had a one-to-one in which I explained exactly that, and we found that it would be much better to raise these as "can you tell me why is this one like this" (rather than "improvement suggestion" that can be invalidating), and do it in one-to-one so that it's not distracting. Collaboration was much better after that
For sure, it's great to have a new pair of eyes and you certainly don't want to tell somebody to keep their challenges and suggestion for improvement for themselves. But it doesn't mean that there's no good way or bad way to do it
The insights that you get from coming at the problem with fresh eyes are invaluable and you really don’t want to waste those. But many things on that list will evaporate once you have a bit more understanding of the project.
(I still like to make “check in a fix / improvement to the dev environment documentation” the first task for a new starter though, as there’s usually a typo or update required somewhere).