TLDR: you can't learn everything, so learn things that help you grow towards the life you want.
I'd start by looking at who says something is "must know" and what they know about you and your career :) Give it the "will it matter in a month... a year... ten years" treatment.
Other thoughts...
- What you need to know to be great at your current role, here and now?
- Where do you want to go in the next 1-5 years? What do you need to learn to get there? This doesn't just mean career skills. What lifestyle do you want? What life do you want? eg. if you want to go freelance, you probably need different skills than going deep into corporate life.
- Have a specific learning plan. If you want, think of it as a learning backlog with priorities.
- Ensure there's downtime where you're just doing things for fun. Without downtime there's rarely enough mental space to learn.
Current role skills are usually pretty obvious and naturally expanded on the job; but it's good to stop and check that's actually happening.
Career direction skills may not be obvious at all and tend to need more training/mentoring/time. It helps if your boss knows what opportunities you are looking for, too (so they can steer the right opportunities your way).
On the purely technical...
- value conceptual knowledge as well as specifics. ie. programming principles that remain valuable across more than one language
- favour standards/basics over abstractions. eg. vanilla js over a framework
- learn a totally different language once in a while, just up to a Hello World/tinkering level. It gives an insight into other ecosystems and usually you can bring something back to your focus language.