The Google Global Site Tag
The Global Site tag is also referred to gtag in the Google documentation. I must say that in my "journey" into the new Google Analytics that I am a little confused into how I determined what the correct tracking code should be.
Never-the-less, GA4 seems to be tracking my pages although I am still using the "Universal Tracking" code and ID.
My suspicion is that Google have changed this and the Google help says that you should only add one instance of the tracking code to your pages and that the IDs are interchangable. You can even create your own?

The Google Developers Overview
The HTML code for the GA4 tag can be seen here. To use it you don't have to know how it works - that is just me!
Background
After adding the Google Global Tracking Tag bck to my pages I was curious to see how it works. This was a new thing to take a look at.
Once again, my humble JavaScript skills are exposed! Still, I did see a useage of the logical OR.