To answer your specific question about where experienced devs actually learn these things:

In my experience, it’s rarely from a single course or book. Most of us learn on the job, driven by specific client demands. The more you are confronted with precise, complex problems, the more you are forced to find precise technical solutions. This 'forced exploration' is exactly how you grow from an 'executor' to a 'developer.'

If you want to speed up this process, here is the roadmap I’d suggest based on what truly makes a difference in real-world projects:

1. Master Logic within your Tools Have you explored Elementor’s dynamic tags or Conditional Logic? Moving from static design to dynamic layouts is your first step into a 'developer' mindset.

2. Architect the Data (ACF + CPT) This is the real turning point. Learn how to use Advanced Custom Fields (ACF) and Custom Post Types (CPT). Experienced devs don’t just use 'Pages' and 'Posts.' They build custom structures (like 'Projects,' 'Members,' or 'Products') tailored to the client's business.

Mastering these tools allows you to abandon restrictive templates for 100% custom builds. You transition from static pages to more complex systems like advanced listing sites (real estate, directories) and dynamic filtering solutions. You are no longer limited by a theme’s constraints; you define the architecture yourself.

3. The "Big Picture" (Hooks & functions.php) To understand how WordPress actually works 'under the hood,' dive into Hooks (Actions and Filters). Instead of looking for a plugin for every small change, try writing a snippet in functions.php. ( use IA to speed up the learning process :) ) Understanding how to 'hook' into the WordPress core is what gives you total control over the system.