[_y5hn]

If you can read and tweak code, you are already useful for 90% of necessary work. For maintenance you have little need for OOP concepts. 95% of code out there is crap anyway. What matters is: Is it being used / is it useful? If you can manage to create such code, you are already competing with the best of the crap. There's never enough time and money to do it right anyway, don't be too hard on yourself.

Recognize how powerful circumstances always are.

There are things you can do to improve or feel better. It needs to be deliberate and you need to care enough to put extra effort into it and manage your training as you would do a project.

Lots of talks on youtube can provide pointers and inspiration. But it's hard to get the chance to put it to use. A hobby project would provide that opportunity, but it need to be something you really want to do and something that will provide you some value.