I did a whole campaign with Lost City, utilising the Goodman Games hardcover, the Elder Evils supplement, and the prequel adventure from Dungeon, Masque of Dreams - which Wizards should honestly have incorporated for their own version.
The Goodman Games version fully detailed all the levels, keeping the sparse details of the original module and expanding them. (The dragon has a name, as does the vampire). My problem with this version is that Lost City is a megadungeon, and truncating it into a short adventure like they've done...
Because the fond memories of your youth must be mined as nostalgia bait for the latest flavourless grey goop that WoTC and its corporate masters will serve you. Don't ask questions, consume content.
Who remembers the Enworld thread voting on who was the hottest iconic? And the controversy on Lidda winning and some posters accusing the others of degeneracy. Usual stuff.
Are we back to this nonsense that the existence of a home game is a priori cause of a multiverse? Is there a multiverse in Call of Cthulhu because people have different home games? No, that's nonsense. This is an explanation is search of an actual conundrum.
None of that requires a "multiverse". Our own universe has multiple planets. Oerth and Toril and Earth can exist just as, you know, different worlds. It doesn't suppose the existence 600 different parallel Elminsters.
It's probably my biggest complaint with Radiant Citadel. Each of the settings is as far as I can say, way too much a direct lift of its real world inspiration, down to artistic choice. "Lived experience" does not mean I want African American authors to recreate 19th century antebellum southern...
Sounds like you don't need to change anything about the existing Forgotten Realms then because all DMs will already change things for their own campaign?