I would agree. Your job is to implement the new features and leave the code in a better state than when you found it.
As a professional programmer, your job is not to produce beautiful code. Your job is to make money.
There is a commercial decision for the organisation to make about paying back the tech debt in this code base. That's not your decision to make. Likewise, it's not your decision to create more tech debt if you can avoid it (sometimes you can't because deadlines are more important than tech debt).
As the parent said, your best course is to implement the new features, and refactor where it makes sense to do that to support the new features. But without any test suite, you risk breaking the existing features by doing anything more than the absolute minimum of refactoring. That's bad.
As a professional programmer, your job is not to produce beautiful code. Your job is to make money.
There is a commercial decision for the organisation to make about paying back the tech debt in this code base. That's not your decision to make. Likewise, it's not your decision to create more tech debt if you can avoid it (sometimes you can't because deadlines are more important than tech debt).
As the parent said, your best course is to implement the new features, and refactor where it makes sense to do that to support the new features. But without any test suite, you risk breaking the existing features by doing anything more than the absolute minimum of refactoring. That's bad.
Good luck. And welcome to the profession hehe