I'm a little unclear about this "fake sound" thing. I'm aware "some" auto manufactures are supplying some type of "external" audible noise that will emit at low speeds. I've heard up to 18 mph. Notice I didn't use the words required or regulation. If it's "regulated" then by who? Self-regulated by the auto industry? Where are these regulations documented and what body wrote and is maintaining these regulations?
Currently multiple auto manufactures of EVs are exploring different sounds. If the synthesized sounds are regulated you would think there would be some guidelines on what sounds they could emit, e.g, pitch ranges, loudness, duration, speed range, etc. I happened to bring this topic up with a friend of mine about a month or so ago who owns a Tesla. He said Tesla hasn't pushed out any sound nor are they required to. (Is he mistaken?)
Next, I've read some articles and watched some videos where they talk about these synthesized sounds from inside the vehicle like with the video for the Mack E in the OP. So is the "industry" looking to synthesize internal and/or external sounds for EVs? My comment above of the user supplying their own sound was based on the sound emitting only for the inside of the cabin. Clearly you would not want the user to pick any sound to be emitted outside of the cabin. Again, regulation guidelines? In addition, note in the Mach E video, the sound continues well beyond low speeds. Another variant to the industry self-regulating these "synthesized sounds?"
I fully admit I have not closely followed the developments (implementations?) of these synthesized sounds. I get the impression no official regulations exist since it appears this particular topic is still being explored within the industry, but I could be wrong. So please pardon my ignorance if some formal regulations exist some where.