In the early 2010s, I read a book about a group of adventurers in Middle-earth who retraced the steps of the Fellowship of the Ring and Frodo, only to gradually learn that the history of the Ring and the Ring Wars were mere lies and propaganda concocted by elves and Gandalf.
I do not remember the specific nature of the ruse or the reason for it (probably to keep the Ring), and that is why I want to find the book and read it again.
Here are the details I remember:
The Ring wasn't destroyed, and Gollum didn't die at Mount Doom. Instead, he was a disguised elf by the name of Gil-gamesh (because all elf names start with "G"). He injured himself in the mountain. Over the years, he became disgruntled and had zero regrets about spilling the beans to the party.
The party of adventurers included a dwarven female who fell in love with Gil-gamesh. They carelessly engaged in a physical relationship because they believed elves and dwarfs couldn't have children, which proved to be another falsehood spread by elves.
Bilbo was in on the ruse, and the story of "The Unexpected Journey" was made up in order to persuade Frodo to do the dirty work.
Moria was much smaller than the Fellowship of the Ring believed, but Gandalf deceived them by leading them in circles.
Sauron was disposed of by an elite commando unit of elves; the destruction of the Ring was not necessary for his demise.
I read the book in Czech, but it might have been a translation... or not.
The book cover was beige/light brown with runes.