Adding a simple meta box to a page

I am a long-time Elementor user and not in the least a coder, although I don't mind working with code if someone else has written it and I just have to cut-and-paste it and perhaps make a few adjustments.

I want to create a page in Elementor that can be easily edited by my client without having to use Elementor. That is, I'd just create fields that would be linked to various Elementor text (or other) widgets on a given page and my client would simply have to change the content of the page's variable fields by entering it into a meta box on the standard (i.e. not Elementor) block editor page.

In fact, what I want to do is pretty well perfectly illustrated in this instructional video, posted by Meta Box!

Unfortunately, the video initially shows the manual entry of a whole bunch of PHP code that presumably generates the meta box. There is no explanation of what's going on here and the actual code appears nowhere for a non-coder to actually copy and use. How cruel! (A person posting a comment on the YT video gets ignored with no response to the same source of frustration!)

Could you please direct me to a resource that would either explicitly walk me through how to do this (with code that I could easily use!) or perhaps indicate a more up-to-date method of accomplishing the same thing, perhaps with no coding required at all. I acknowledge the YT video being three years old, so things might have advanced in the past few years!

Thanks in advance for the help.