What is the pathway to be a full stack developer in 2021?

I really like to learn creating websites as a one man team, I like to create shops but I want to be able to do more. After some searching I concluded that I have to be a full stack developer (I love the programming flexibility instead of using CMSs). I don't know much about some concepts like mobile-first dev, but I do know HTML, CSS, JS (not ES6), and PHP.

- Is that a must to be a full stack developer in order to create websites without using CMSs and website builders? If not, what should I do?

- What are the approaches and which one do you recommend?

- What kind of stack should I choose and focus on?

- How much can I do on my own? What's the limit?