Looking for Backend Course Recommendations Focused on Fundamentals

I'm diving deeper into backend development and I'm finding that many courses jump straight into frameworks without really breaking down the underlying principles. For instance, tutorials often start with frameworks like Express, Django, or Spring Boot, but I'm still a bit lost on the basics like how APIs function, the fundamentals of HTTP, authentication flows, how databases work along with querying, Linux and terminal workflows, and Git for version control. Is there a well-structured backend course or learning path that emphasizes solid fundamentals before just connecting various libraries? I'm not looking for a complete bootcamp, just something that actually helps build understanding and practical skills. For those who have focused on backend development early on, what resources or courses did you find most beneficial?