I think I can honestly say that building a bunch of side projects has made me a better developer. I get to actively work on different problems, try new things and improve my knowledge.
Have one specific project, a project you know exactly how you want it to work, to test out new ideas, technology and frameworks on. If it contains multiple parts, like interacting with an [[API]] or how to contain state, it's a perfect project to evaluate new technologies with.
You can potentially learn even more by [[Learning in public]]