This game actually does have a separate set of objectives to get 100%

To 100% the game:

Collect all the gems in each level

Play the toybox minigame unlocked after the credits

Collect all 30 "Friends" that randomly appear when going back through levels. You can check which friends you've found by talking to a new NPC that appears in the hub post-credits.

Collecting the friends takes the majority of time in the run. I spent 21 minutes on the friends and 14 minutes on everything else.