To study object-oriented programming beyond grammar again? - - UML?

Until now, I have never done proper object-oriented programming as a job.

So far, the only programming needed was procedure-oriented Python and C programming.

c++? I can simply create, inherit, spin, etc. classes.

I only did embedded programming with C, but I never did C++.

But suddenly, after the existing project, I'm putting it into a new project, so I'm doing a flashy programming with C++. Everyone else is good, but I'm the only one dying.

I'll just do simple C++ grammar, data structure, STL, and so on.

The problem is, it's beyond that.

What I'm lacking right now is the adhesion between objects that I learn while teaching UML, and the relationship between objects.

I don't even remember what I learned in school, but what do I need at this moment?

What should I look at in a hurry? You know by showing the structure diagram, etc. between each object, right? I do, but it's frustrating.

I definitely feel like I learned it in school a long time ago

Books or lectures - it doesn't matter if it's a paid lecture - I'd appreciate it if you could give me any direction.

I'm passionate about learning, but I don't know the direction, so I can't move on.