I’m a mid-level backend dev, ~3 years YOE. I wanted to seriously start thinking about expanding my skillset and learning new stuff / new technologies outside of my daily tasks. But I’m unsure of how to start, how to decide, what would be most helpful to my career, etc. Any advice?
Solid advice. Try something tangentially related to what you do, at a sufficient but comfortable distance. This will help you grow as a developer. Also totally seconding the last line - it must be fun.