What development strategy is optimal for professional and career growth of a java middle developer?

Question

Java

The trajectory of growth from junior to middle is quite clear: getting your hands on typical tasks, expanding your IT horizons to an acceptable level, gaining basic architectural skills, etc. But in what direction is it better for a java middle developer to move?
For example, I have a desire to improve my knowledge of front-end technologies (learn React, improve CSS, etc.), because I would like to feel like a specialist who, if anything, can make a web application completely with his own hands. On the other hand, I understand that I will not be a front-end developer, but a specialized specialist will still do it faster and better. Therefore, the question arises, is it worth spending time on this?
Similar doubts arise when you want to dive into devOps (Jenkins, Ansible) and database architecture (execution plans and query optimization, deeper study of NoSQL database architecture).
How do you think middle should be developed?
To grow first of all "in breadth" (for example, to study the front for a backender) or "in depth" (for example, to take Hadoop and study it to the smallest detail)? Or is it worth paying attention to pumping more general skills (for example, managing a development team, development methodologies, or building and analyzing the architecture of information systems)?
Which aspects of development, in your opinion, are critically important, which ones are simply desirable, and which ones are not worth spending time on at all?