It's not supported on Mac/iOS. Apple's solution to this was going to be WebGPU, but it's been in committee hell for way too long, and Apple is seemingly intent on torpedoing any goodwill they have left.
Google has since picked up the slack and is working to add WebGL 2 to WebKit on Mac/iOS platforms.
Just to be clear, it is not supported on macOS Safari, but WebGL2 works with other browser engines. On iOS, there are no choices however because all browsers have to use the provided Apple one behind the scenes.
I'm not sure how to interpret your theory of what is happening behind the scenes - Switching WebGL to use ANGLE on Safari/WebKit is a Google-led project and Apple is "meh" on it?
Your link is just talking about the feature being blocked on the ANGLE switch.
