Looking closely at the NovelUpdates review, using the 'shifting reverse harem trend' to justify this ending doesn't really hold up when you look at the actual logic of the story. The spoiler clearly states: 'She is staying at Mount Hwa, and history will remember her and her lover as 'best friends'. ML accepts this fact.'
From my perspective as someone who reads the spoilers, by trying to have it both ways—keeping the MC strictly loyal to Mount Hwa's celibacy rules while secretly giving her a lover—the narrative completely blurs the boundaries of what a mono-romance should be. When the actual Male Lead is stripped of his official romantic title and downgraded to 'best friend' status in the eyes of the world, he is effectively placed on the exact same level as the other childhood crushes and platonic friends in the story. If the main romantic relationship itself isn't allowed to be recognized as official, then the story accidentally validates the reverse harem tag. It literally becomes a 'friendship harem' where every single guy, including her actual lover, just looks like another close male friend hanging around her at Mount Hwa. You can't call it a proper romance when the romance itself has to masquerade as friendship just to exist
Well, you might have a different opinion and perspective than me. Feel free to enjoy the manhwa, though!

Man, just found out the novel is actually a reverse harem without "end-game" male lead... ╮( ̄▽ ̄)╭
It's not my cup of tea.. Sigh