So, this idea is simple. It's the ability to, using a creative command, completly fill the book, so you know all the recipes. For those willing to have spoilers, and learn the more intriciase of mechanics, not discovering (So, someone could find how to optimize ratios, and bypass finding every recipe first)

This is already possible! To disable the advancement gating entirely, go to config/patchouli-client.toml and add reactive:journal to the noAdvancementBooks list. This will reveal all entries.

If instead you just want to 'cheat' past one advancement block, but leave the rest intact, you can give yourself the relevant advancement. This is done using the /advancement grant @p only reactive:(advancement_name) command to give yourself one of the reactive advancements. The advancements aren't named the same things as the pages they unlock, so it might be confusing to find exactly the gate you want to open. I'd recommend the first approach.

You might also be interested in the client config option that shows all Power sources in JEI, located in config/reactive-client.toml

okay. Thing is, I used /advancement grant @p all...

That would also work but it would mess with other mods and the vanilla advancement track... All the pages should be unlocked in that case though