Here’s a clear breakdown of what that update and DLC situation includes:
It sounds like you're looking for information on on Nintendo Switch , specifically regarding update/patch version 1.1.0 and DLC content after an update.
For the first time, Amy is playable across all four main titles ( Sonic 1, 2, 3 & Knuckles, and Sonic CD ) with her own unique "Jumping Hammer Attack". Playable Knuckles in Sonic CD:
