How can I move past the intermediate programming plateau and finish real projects?

It is easy to become stuck after learning object-oriented programming because you start worrying about patterns, abstractions, and whether every class is designed correctly. That can make simple projects feel impossible. Try setting those concerns aside and write the simplest code that solves the problem. You can refactor after it works, and you may find that you prefer a simpler or more functional style rather than forcing everything into elaborate object-oriented structures.

Honestly, I am not writing much at the moment, which is probably part of the problem.

The most effective way through this is to choose one small project you actually want to use and keep working on it until you have a functioning prototype. You will need to look things up constantly, but that process teaches you what you really do and do not understand. Finishing something also builds confidence that you can solve unfamiliar problems instead of needing to know everything in advance. Design Patterns, often called the Gang of Four book, can be useful later for learning common object-oriented solutions, but it is much more valuable once you have encountered similar problems in your own code.

The biggest issue may simply be that you are not writing enough code yet. Stop searching for the perfect resource and build small things you would genuinely use. Expect the first versions to be messy, finish them anyway, then repeat with a slightly larger project. Confidence usually comes from completing projects and learning how to investigate problems, not from reaching a point where you feel completely prepared.