So within my own area of the codebase and tech stack I own, I'm very comfortable and confident leaving feedback and sharing thoughts. However, I know that in order to grow to senior, I need to expand past my immediate area into other spaces like the components and services built by other teams in my org like sister teams. For those areas, I'm unsure how to share my thoughts since I'm not an expert in those codebases. So let's say I come across a code review from one of these more "separate" areas from my own and the engineer behind the diff is more senior than me - How can I leave my feedback in a way that respects the situation?
Start with what you know. Sometimes the best code reviews I received were from an engineer coming in from another part of the stack, since their perspective was novel. For example, you could say "In the Android side, we centralize the JSON validation in one place at the networking layer, so the product teams don't have to do null checks. I'm curious how you handle that here?"
Another tactic I like to use is to end almost every code review comment with a question mark. This leaves room for you to be wrong, and is much more about learning rather than a declaration. This is especially important in this scenario since you're entering into a new codebase where you may not be as familiar.