'What is the element of lore of each particular franchise supposedly being broken, and how?'
In Lord of the Rings: The Rings of Power, people claim there were no dark-skinned dwarves, yet a dark-skinned woman was cast as a dwarf. There are other complaints regarding Galadriel and the other elves and how they act 'human', as well as Galadriel being an action heroine.
'Mary Sue is a concept only meaningfully applicable to fan fiction. Apply it to canonical works makes no sense.'
Well, in their defense, the protagonist of the Sequel Trilogy Rey has no flaws or character defects. She is able to effectively use the Force, wield a lightsaber, and pilot the Millennium Falcon despite having little or no prior training.
'I can only say that I do not support tokenism, which in essence is degrades characters into props and thus insults the very minority being tokenized.'
Precisely.
Incidentally, what is your opinion on the animated series Steven Universe? It was made by a Jew, but it has received critical acclaim for its LGBT representation.