Yes, there are definitely jobs where you are writing more new code than maintaining, upgrading, bug fixing and improving old code (startups without product market fit being one, consulting being another) but in general code is expensive and folks want to run it for a long time.
This is a good way to start improving a codebase because it has minimal impact on the actual code.
Tests help you write maintainable, extensible code that others can change fearlessly.
If you run across code that isn’t tested and you have time and the supporting framework to write one, do so.
It’s sometimes a winding path, but upgrading your dependencies regularly is a good way to maintain the code.
It never feels good to spend time updating a dependency; to me this always feels like running in place.