To be a great software developer you need to work on pet projects for yourself and for others. Some people do the 9-to-5 and that's fine. But those are going to be your median developers. Not your great developers.
Nothing wrong with that.
Great software developers are great because they sharpen that edge for fun. They straight up love writing code.
When you work on pet projects you research new tools, new ways of doing things, and broaden your horizons. You open source stuff, forcing you to write clean code with proper documentation.
That _directly_ influences how you write code for your job. That knowledge applies in strange and unexpected ways. In my experience you end up using a lot of the new stuff you pulled in through your escapades.
You want to be a great software developer? Write open source code. Read open source code.