For intermediate Korean learners, how should one study?

Hello! I am currently an intermediate learner of Korean. I have been studying Korean for about 4 years and took Korean classes for 3 semesters at university. Since then, I have mainly been exposed to the language naturally through Korean dramas and music. Recently, I received a 3A on the Korean level test from the Sejong Institute, and while I can communicate at a basic level, I feel that my grammar is weak. I have a basic understanding of grammar, but there are still areas where I lack knowledge, and I feel overwhelmed about how to proceed with my studies. I find it particularly difficult to understand long sentences, and there are so many grammar concepts that it can be overwhelming. I think I need a more systematic learning method, and I liked the structured approach of the university classes I took before. I currently live in New York, so I am also curious about what resources or classes are available locally. I want to find ways to better understand and use complex grammar and vocabulary. Please recommend books or classes suitable for my intermediate level. I would appreciate any advice!