[Chyzwar]

You should focus on two things:

1. Your "personality"

Properties/qualities that you like most. To discover what you really like you need to try different things. It might change over time as you become more experienced.

  - dynamic vs static
  - weakly vs strongly
  - oop vs functional

2. Impact and market.

You need to specialize in things that let you make the most impact. At some point, knowing specific APIs/Frameworks is more important for productivity. You also want to get nicely paying job and these will only come when you are expert.

  - frontend vs backend 
  - DevOps vs dev vs dba vs full-stack
  - networking vs distributed vs graphics vs web vs embeded

I would avoid Project Euler as problems are too small to evaluate anything other than syntax. Learning stuff like Kube or AWS is not particularly useful. Knowing what tool to use and how to put it together is more important.

Finally depends what you choose you might end up learning one language or multiple.