Hard to answer without knowing what you want to do.
If you want to become a better developer, then maybe go deeper into your current stack. Can you package an application? Write a full suite of tests? Optimise for memory/runtime? Know how your language compiles (Python)?
If you want to become better rounded, try a different language to what you’re familiar with. If you write Python, consider a statically typed language. Or functional programming.
If you’re a data analyst, can you setup data pipelines?
There are a ton of things you can learn, but it’s hard to recommend one without knowing what you want. I think SafariBooks is a better resource for in-depth learning, while PluralSight is good for intermediate or follow along type tutorials. Udemy hS been for more “intro to” type stuff.