What is the best Spring course?

To answer your questions, Spring is easy to learn because the whole framework is designed to work with POJOs, instead of relying on special interfaces, abstract classes or such.

6 Best Spring Framework Courses for Java Developers in 2022

To learn Spring Framework Basics like Dependency Injection, Bean Life Cycle, Autowiring, MVC, AOP(Aspect Oriented Programming), it should take around 50+ Hrs , assuming spending about 2 to 3 hrs, in about 30 days(approximately) & it also depends on your prior expertise/experience, you will get some confidence.

Since most of the developers want to learn Spring MVC, I suggest you first start with Spring Core and then follow the Spring MVC part.