What is an "adventure hook"? And is that a "diegetic" concept - do people in the imagined world of your RPGing really wander around looing for "hooks" to motivate them into adventurous action?
Sometimes, yes they do.
A party that finds itself at a loose end and with nothing obvious on its plate might put out feelers as to whether there's any jobs or missions need doing; and if there are, whether those missions are within what the PCs in-character think they can a) handle and b) be interested in doing.
In my settings the PCs are most certainly not the only adventurers out there; and the different classes tend to more or less loosely associate in guilds. There's mercenaries' guilds for warrior types, mages' guilds, thieves' guilds, bard colleges, monk monasteries, cleric temples, and so on; and some of these tend to become hubs for "news" about adventuring possibilities (and that news may or may not be the least bit up to date).
Thus, a Fighter in a party looking for adventure might head down to the merc's guild and there hear rumours of Orcs raiding farms in the western hills, that Giants have been sighted in the Kertchen Pass, that the old Argoth Tower has lit up again, and that a group of neophyte adventurers have failed to return from a trek into the eastern forest.
Investigating these rumours might reveal that someone's long-since already gone to (in theory) deal with the Orcs, that the Giant sightings have been confirmed and are becoming more frequent, that there's a long and sorry tale around what happened the last time Argoth Tower showed signs of life 30 years ago, and that a lone survivor of the missing party wandered into Lelivil (a small eastern village) last week with no idea where she was and speaking of tentacled horrors beyond imagining.
From here the players would have their characters, in-character, decide if any of these possibilities appealed, and if yes they'd take steps to folow up and get involved. If two or more missions appeal they might even split the party (and recruit more characters to fill out both groups, if needed) and try doing both (at the table this would translate into playing one group through its mission then we'd flip to the other group and play through their mission). If none of the missions appealed, they might try their luck elsewhere pr just decide to take some time off.
