I have basic knowledge in HTML/CSS, JS, PHP, some server-related stuff, where do I go from here?

On an on-and-off basis I've been making simple websites since the year of 2003 or so, always was more or less a hobby, made SOME money on the side with it and actually that knowledge even secured me my current non-dev job, because it's just useful for what we are doing here.

Still I really always wanted to dive deeper than where I was, especially because of where the WebDev technology is right now compared to my beginnings. I still remember how it always used to be a pain finding a resolution sweet spot, how IE was still so wide-spread among users, how stressful the workflow was back then in general - that killed much of my Dev vibe at the beginning. Today the workflow itself is just fascinating enough for me to keep me interested. Version control, pre-processors, reliable package managers like npm, brew etc.

To give you guys an idea of what I can do:

• HTML/CSS with latest technologies like flexbox and grid.
• PHP: build easy PHP backend solutions for user interaction. Worked with certain frameworks like Zend and Larave with relational DBs.
• Javascript: very basic Vanilla JS knowledge, I am one of the lazy guys who tend to still use jQuery even for the most simple tasks
• Configure a server with the command line or administration tools like Plesk/Webmin, implement SSL certs.
• Install and customize Wordpress Websites (that's an easy one).
• Simple SEO onpage optimization
• I feel at home in the terminal/shell and in the OSX / UNIX environment.

I have no clue where I could go from here. What should I learn that is an immediate "value-adder"? I like the idea of JS Frameworks like Vue and/or React, but they seem to be of little use for developing small one-page websites with rather static content, right? I also like the whole Node.js world and I wanted to start learning everything that goes into the MERN (Mongo, Express, React, Nodejs) stack, unfortunately the mern.io project seems dead and deprecated.

It seems to me that there is a very high skill cap for everything that would come naturally from my status-quo.

Although it is still more a hobby than a job, I went from a strictly finance-related job to a techical account manager job. I want to develop my skills further to a point where I can maybe one day become an IT/WebDev Project Manager, for example.

Merry Christmas and THANK you for any input in advance.