Running through `git blame` and looking at the commit message, the PR, and the PR comments is a very practical way to learn about a codebase! Beyond some high level code organization stuff that exists in a readme, learning a codebase is really about getting a history lesson of how the product evolved, the company pivoted, and the team re-org'd.

It'll be 6-months if you're lucky. Try figuring out why there's a particular "if" clause, one or two or four years later. Software maintenance, especially when the original author has moved onto another team/organization/company/career, is a frustrating art of almost remembered stories and hoping that you can figure out Chesterton's fence, lest it become Chesterton's barbed wire. The worst is when you fix a small bug with code and introduce an even bigger big in the process.