Captain Toad Treasure Tracker is without a doubt is truly a fun game. Tons of hidden items and so many tricks if this is the last games for the 3DS Nintendo certainly created a brilliant game.
As to the details:
Episode 1 has 18 levels
Episode 2 has 18 levels
Episode 3 has 28 levels
Bonus has only 4 but only can be opened by using a Super Mario Odyssey Amiibo.
There a total of 68 levels in the 3DS version. The Switch version has more levels depends on the current DLC.
The Amiibo aspect of this game is interesting, besides what I previously mentioned about the Super Mario Odyssey Amiibo.
The Toad Amiibo gives you invincibility
Any other Amiibo an extra life.