@StefanL38 ,
Topics split as requested.
There's no solution to this, if there was it would be pinned at the top of introductory tutorials and everyone would link to it for beginners. The problem, as I see it, is that different people learn in different ways, so no one tutorial is right for everyone. Add to that, even if there were some super good easy to understand tutorial about non-blocking code and timing it would of necessity be generic. Each person asking a question that leads to teaching about non-blocking code has their own unique problem and their own unique way of not (yet) understanding the need to write in a way that is multi-tasking.
The purpose of this topic: Flashing multiple LEDs at the same time was an attempt to address some of the differences in learning styles by demonstrating non-blocking timing in several different ways in the hope that if someone who is struggling with the concept will understand at least one of them. Whether it worked is for others to judge.
Your efforts to resolve this eternal problem are valiant and appreciated, and I hope one day to see that elusive super good tutorial we are all searching for.