I wouldn't say exactly "against the lore" as much as "against the tone". In LOTR, like in many other works of fiction, the most wonderful powers in the universe are only allowed to show of in very rare ocassions. This allows the reader to stay ever-amazed at their incredible power.

When you break this sheme and make amazing feats occur regularly, they stop feeling amazing at all. Take Dragon Ball for example: in the first saga the dragon balls are a collection of misterious arcane artifacts that nobody every has gathered together, and the first time Shenron shows up it is considered a HUGE deal; In DBZ the balls had been gathered so many times that fans make jokes about how many times Krillin has been resurrected, and Goku after defeating Cell chooses not to be resurrected as matter-of-factly as someone would choose their tie for a meeting; In some OVAs they collect all balls in a 20 second montage, and by DB Super, the dragon balls are such an ordinary idea that Bulma collects them a fucking prize for her birthday raffle like some common piece of IKEA furniture.

When a new writer approaches an established universe, it could occur that they follow the rules of the universe to a point, but still they will fail to respect the proper tone of scarcity of things that were Big Deals™ for the original author. This happens so much in fanfiction when authors create original content, that a term has been coined to refer to it: The Mary Sue, the can-do-all fanfiction OC that is oftentimes a wish-fullfilling self insert of the authors who give their avatar every single cool trait they love from the original material. That is how you get those absurd OCs everybody laughts about, like "the secret daughter of a Ninja Turtle and Supergirl who can do nijutsu and fly and is pretty and became inmune to kriptonite thanks to her mutant blood because I never understood the concept that a perfectly unbeatable hero is as interesting to the reader as watching wallpaint dry".

But such attitude is not exclusive of fanfiction. You will have this sort of thing everywhere from DnD players that min-max their characters to the point of making their game boring, to principal authors that do this sort of thing to their own universes either because they do not know better (Eragon, anyone?) or to do a cash grab (aforementioned Dragon Ball, arguably JK Rowling too)

To me SoM seems to have this second type of writing. Like, the writers have probably read every piece of lore in existence and undestand how magic and spectres work in the Tolkien universe. But then they decided to approach the lore material from a "try to game the rules to make the most OP protagonist I can" point of view rather than "try to make my protagonist representation fit in what the original author wanted to say about the nature of humanity and choice between good and evil".

I would say that "A half human-half wraith walking into Mt. Doom and crafting a new Ring of Power" is an idea that is perfectly "possible within the rules of physics of the Tolkien universe", so to speak, but is still a terrible idea if one wanted to write an "apocryphal Tolkien story", that is, one that feels like it could have been written by the original author.

All this is not incompatible with the game being super fun, and even the story being interesting on its own terms. But when a LOTR fan reads the sinopsis of SoM, they feel like they are being told one of those jokes when a genie offers three wishes to a human and the human wishes for infinite wishes and after that a wish means nothing special at all.