What has changed?
Adaptive Images used to have an explicit dependency to version 2 of the SixLabors.ImageSharp NuGet package.
This has been replaced with a dependency to version 2.x of the EPiServer.ImageLibrary.ImageSharp NuGet package from Optimizely, which effectively means a transitive dependency to ImageSharp V3.
Why the change?
There are two main reasons: to align with Optimizely's use of ImageSharp and to avoid Adaptive Images requiring its own ImageSharp license.
Adaptive Images isn't by itself relying on ImageSharp, but is instead designed to make use of Optimizely, and its peripheral services like the CDN, for image manipulation. If Optimizely moves away from ImageSharp, so will Adaptive Images.