Good for you for finally providing some details.
Sorry I can't help you out.
I manage my entire media library via iTunes on my Mac and have done so since the 3rd generation iPod (scroll wheel, circa 2003), long before there was any iPhone or other iOS device. Playlists aren't some ultra-secret hack or undocumented feature. They've been around way longer than the iPhone.
If I recall correctly, the original iPhone did not have a built-in music store. It could only play music that was synced from your computer's iTunes library.
If anyone here is a fuddy duddy, it's me, not you.
My Mac's iTunes manages the media library for my iPhone, an iPad, an iPod touch, and an iPod classic. This includes podcasts (another media category that precedes the iPhone).
Anyhow someone else will need to chime in, but now that you provided some pertinent useful details, you might get some more valid responses.
Since I manage my media content in a manner that is totally different than the way you handle yours, I hereby bow out of this discussion.
Best of luck and thank you.
P.S., The iPhone 4 is not officially supported on iOS 11. Note that this phantom Google source that you are quoting may be referring to instructions for a version of iOS that your iPhone 4 is not capable of running. You should mention what version of iOS your iPhone 4 is running. That might also help.