Learning to deal with "unmaintanable" codebases is a pretty good skill. It taught me good documentation and refactoring manners. It's only a problem for you if management does not accept that their velocity has gone down as a result of tech debt pilling up.

Code should scream it's intent (business-wise) so as to be self-documenting as much as possible As much as possible is not 100%, so add comments when needed. Comments should be assumed to be relevant when written, at best. Git comment should be linked to your work ticket so that we can figure out why the hell you would do that, when looking at the code file itself. I swear some people seem to think we only read them in PRs (we don't). Overall concepts used everyday, if they need to be reexplained, should probably be written down (at least today's version). Tests are documentation. Often the only up to date one?