Does "know more about something" really mean "more" (implying that one already has some prior knowledge) or just a customary phrase

It is a question resulting from a translation attempt of this sentence:

Many, however, may wish to know more about this remarkable people from the outset. (Lord of the Rings, Prologue)

From here we can see "from the outset", which indicate that they had not prior knowledge of "this remarkable people".

While we also see the familiar expression "to know more about". Does the "more" here imply that one already know something, but only wish to have more additional knowledge of it? Just as in "I want more water" means one already have some water and "I want water" means one didn't have water before.

It's a nuance difference but there's a debate going on about whether the "more" could be omitted from the translation. Hope to get some help. Thanks!

I don't have my Tolkein right in front of me, but I would interpret this to mean that Tolkein has already given a very brief description of the people of Middle Earth (or maybe just Hobbits) and postulates that many readers might want to know more right away rather than jumping right into the story narrative.
I interpret "from the outset" to mean here, at the beginning of the story, and not necessarily implying that absolutely no information has yet been provided about the people of Middle Earth. On the contrary, as you point out, the "more" would indicate some small amount of information has already been provided.

"Concerning Hobbits", the first section of the prologue of The Fellowship of the Ring, from which the quotation in the question was taken, begins:

This book is largely concerned with Hobbits, and from its pages a reader may discover much of their character and a little of their history. Further information will also be found in the selection from the Red Book of Westmarch that has already been published, under the title of The Hobbit.

Then there's one more sentence describing very briefly the nature of The Hobbit, and then the quoted sentence.

So in this context, "know more" means know more about Hobbits than what is learned from The Hobbit.

If you changed the sentence to "many, however, may wish to know about this remarkable people from the outset" it would make the mention of The Hobbit in the two prior sentences unnecessary, or confusing.