Man, my nephew hit that 'I'm bored with everything' phase last summer, and the books that actually stuck were the ones that felt like a video game you could read. 'The Last Kids on Earth' series was the gateway – it's basically zombie apocalypse meets treehouse fortress, with gadgets and mild gross-out humor. He tore through those. Also, the 'Wilderlore' books by Amanda Foody have that Pokémon-esque 'collect magical creatures' vibe but with higher stakes and actual journeys. For classic adventure, the 'Ranger's Apprentice' early books still work; the survival skills and bowmanship details hooked him more than I expected. Graphic novels like 'Hilo' or 'Dog Man' got reread until the covers fell off, but they count as action in my book – the pacing is all pratfalls and narrow escapes.
What's interesting is that the 'adventure' part needs immediate tangible goals for that age. Finding a hidden city, escaping a monster, building something cool. Philosophical quests or slow-build tension just don't land yet. I'd throw in 'Treasure Island' adaptations too, if the language is modernized – the mutiny and treasure map elements are eternal.