So I was asking bing about seeing is a post field was an empty string and this was its response. It is very detailed and I probed further but I got more and more confused. Is it true what it says here? that in this case "true" and "!== false" are not equivalent?

I’m looking for a good resource to learn how to program with Wordpress. No just themes, or just plugins, but a developer-users understanding of Wordpress so that I can know how to best take advantage of what’s built in and how to build what isn’t there. Any book or course suggestions?
I don’t find the resources on the Wordpress website super helpful.