How to become a “complete” backend specialist?

Question

PHP

Making some progress at the current and past place of work, I decided to completely and completely connect my professional activity with back-end development.
I chose PHP as the main language, MySQL as the DBMS, but there will most likely be options here.
Of the topics for study, I noted for myself:
- One of the frameworks on the chosen PL (I chose Yii2. It may not be the best choice, but it is very convenient for me to work with it)
- Testing
- Linux using Ubuntu as an example
- Security basics in web applications
- Protocol HTTP - implementation from and to, status codes
- Redis, as the main NoSQL DBMS
- Theory of databases, their architecture and design
- Implementation of high-load systems
- Building a REST API
What else can you learn?
What projects to implement for practice?
How critical is knowledge of algorithms?

Answer 1

The map has not been updated for a long time, but maybe you will find something useful for yourself Back-end development map
For practice, I recommend taking something from this list build-your-own-x , you can see how to make a simple web server, search engine, database
Plus here's another article Don't Kill Your Motivation: Master Ruby on Rai... even for Ruby, but there is a list of interesting projects

Answer 2

don't become

"finished"

a valuable specialist, always growing and overtaking ... not necessarily in everything, at least in something (and better in demand)

Answer 3

As for practice, it’s better to look at what difficult tasks back enders perform