Falls under “freedom of overflight,” which necessitates that when entering another country’s EEZ you must

shall have due regard to the rights and duties of the coastal state

shall comply with the laws and regulations adopted by the coastal state

Source please, because the UN convention text says the opposite, the coastal state has all rights to fishing and the creation of oil rigs and artificial islands, but that's it.

Otherwise:

1. In the exclusive economic zone, all States, whether coastal or land-locked, enjoy, subject to the relevant provisions of this Convention, the freedoms referred to in article 87 of navigation and overflight and of the laying of submarine cables and pipelines, and other internationally lawful uses of the sea related to these freedoms, such as those associated with the operation of ships, aircraft and submarine cables and pipelines, and compatible with the other provisions of this Convention.

Ergo, other than what's expressly stipulated (fishing, artificial islands and oil rigs) it's the same as the high seas (article 87 is the one that says anyone may do anything in the high seas), and:

No State may validly purport to subject any part of the high seas to its sovereignty.

Source.

Again, as I’ll repeat, flares are literally described by the FAA as a way to intercept aircraft. The US has used them against Russian aircraft, but in fact the US also does so to intercept civilian aircraft!

What about, what about, what about. And no, the FAA does not say that an interceptor may dispense flares in the way of the intercepted aircraft close enough to create danger for either aircraft. It can use them to get the pilot's attention as a signal, that's all. Just as it is in the video you linked, the fighter dispensed a single flare in the view of the GA plane, at a safe distance. The flare was almost to the ground by the time the aircraft came into view. From your source:

If the aircraft of interest does not comply, the interceptor may conduct a second climbing turn across the intercepted aircraft's flight path (minimum 500 feet separation and commencing from slightly below the intercepted aircraft altitude) while expending flares as a warning signal to the intercepted aircraft to comply immediately and to turn in the direction indicated and to leave the area. The interceptor is responsible to maintain safe separation during these and all intercept maneuvers. Flight safety is paramount.

And about

“breach of Chinese EEZ” (Peter Cronau, ABC)

This is literally a tweet from someone working at ABC, says that "military activity in EEZs are illegal", forgets to mentioned that this is literally only said by China and North Korea, and runs contrary to the UN agreements.

Sorry, but you really come across as arguing in bad faith, and trying to find flimsy justifications for the Chinese crew endangering flight safety and claiming rights they do not have, EEZ or not, by taking random snippets from places and pretending the rest isn't there.