Would the "Dungeons & Dragons : Player's Handbook" be a good substitute if Larian will not provide any form of manual?
As someone new to 5e for BG3, I’ve personally found reading 5e stuff online really, really useful in getting my head around the game, though you do have to stay aware that Larian have homebrewed a number of things so the game doesn’t always work exactly how you’d expect just from reading the 5e rules as written.
I’m not familiar with the PHB as a physical item, only with information from it that is published in various places and formats online, but from the latter I reckon that if you really like having a physical book you can read through to help you understand the game, it might help scratch that itch.