Learning requires context.
If the player knows little, they will absorb little from reading a book. If they know a lot, much of the book will be things known to them, but they are capable of finding something new and interesting from it.
Thus for a bit of book, you should have some lore ready. Maybe at different "depths" with different DCs.
The player makes a roll, and they are told a general overview ("the book is about the history of grain shipments in the middle kingdom") regardless. Then as a result of the check, you say:
Of particular interest is a passage about the Lord of Starlight. He appears to be a Fae noble with some connection to the Far Realm. This passage in particular:
and insert some in-universe prose.
Character knowledge is not the same as Player knowledge. The Player reading the book of lore could get more or less information than the Character should.
By passing out snippets of lore, plus having skill checks on demand, you can provide the Player with the knowledge the Character has as needed. And avoid long dry expositions.
You can see this effect in many works of fiction. A character reads a long book, but they don't transcribe it into the fiction. Instead, useful bits of information are transcribed, often quotes.
Also, you can hand out tokens. Read a book on the trade between Turath and the Fae? Get a token about it; later, you can use it for advantage on a check involving Turath or the Fae. Sort of a limited-use inspiration.
You can limit a character to a number of such tokens equal to their proficiency bonus, representing how many such things you can keep in your head at once, and only on trained skills. Players will then be encouraged to research things they think are useful and match their character's skills, but not everything, to get these tokens.