If you're looking for the full stack and if you feel you're missing something, I would suggest Python, that will really give you a lot more sense of Logic and the sense how things end up on the back-end and this also can extend your knowledge into Databases, Security and AI, of all things ha!
The engineering part I can understand, I've always had a knack for this and architecture and back-end is certainly more of this, as on front-end we take things like connecting to a database for granted, where as back-end you need create the table, the data and then work out where you need to pull it from in a sense into views or urls to be able to display that data correctly on the front-end.
I started with JavaScript, and it just was not going in, someone recommended me Python and within space of two months I picked Python up and then went straight onto the Django Framework (Full stack framework), I hear it might be compatible with React or Vue and Angular.
The weird thing is, after I got the Python down, I could then read JavaScript easier. It's because JavaScript and Python run almost on the same patterns for the syntax's so this has also opened the door to php for me (which also struggled to learn years ago).
Would also suggest looking at the MVC (Pattern), this is important if you're working on the back-end because if you don't understand it then you will get confused.
I wouldn't recommend a course for the back-end simply because by the time you do the course, they're all out of date, as well as tutorials. I would recommend either googling or buying an old book / version to get you started and you will get there.
I have tried courses from:
Pluralsight, Udemy (premium courses) and also out of date..
Be good to follow up how you get on :)