I added the newest version of the datapack to my singleplayer world, and all the function commands appear and I can give myself the book with the command, but when I try to use it it says "Unknown scoreboard objective 'as_trigger' "

Not enough information, cannot reproduce.

I had the same issue. it was caused by a different datapack having a broken minecraft:load tag, which then made it not load any other datapack's load functions