I apologize that this question is inherently vague; I am still in the very early stages of planning a series and don't have many details to offer as of yet.
One of the things that irks me most about some modern film series is that the writers often seem to invalidate the past growth of characters at the start of a sequel, so that they can grow more in said sequel. For example, this happens a lot in the MCU (which is notorious for bad writing, I know, but it's a good example of it); for instance, Bruce Banner in the Incredible Hulk ends the movie seemingly happy with his relationship with the Hulk, but in the Avengers he doesn't have much control over it. By the end of the Avengers, he seems to have developed a better relationship with the Hulk, which was his arc in that film, but this is thrown away in the next few Avengers movies as he once again struggles to control the Hulk. This feels annoying and repetitive as his previous growth is invalidated as soon as a new movie comes along.
I am hoping to write a long series of stories focusing on a cast of central characters. I want the stories — though set in an interesting fictional world — to be extremely character-centric, and focus on multiple arcs happening with multiple characters in every book. Obviously, the main character would have his own character arc every story as well.
I am wondering how I can create a unique & satisfying character arc for my main character for each book. Something that feels like a unique challenge for that story, builds off & doesn't invalidate previous arcs, and leaves room for improvement in future arcs that still allows for a pleasing ending to the current arc.
Any advice is appreciated, and any examples of a popular series where this is done well would be very helpful!