OOP is optional, but so are all other paradigms. You get the cleanest code when you have the most tools for describing what you want to do to the computer. Most JS devs just use arrays for everything.
I wish this was more widely understood (that's it's merely a pattern, not an inevitability), so much OOP code is just bags of arbitrary stuff. It's not an inherently bad pattern, just often misused.
With respect to the warning, MDN has a compatibility table at the bottom which shows full support on all tracked systems since very early version numbers.
Symbols + Maps have some neat gotchas that are good to be aware of.
For example, if you use Symbols as keys in an object, Object.keys() or for...of/in will NOT return/iterate over those keys. You have to use Object.getOwnPropetySymbols()...
I skimmed through it too quickly, but it seems that most of these links are rehash of ES6 spec, which is pretty technical but understandable. If you have no issue with technical details and (like me) do not want narrative, you may refer to it as well.
There were several things on that list you never need. 14-18 is for OOP which is fully optional in the language.