Most of this should be covered by DSC documentation;
However PS Core exposes several public APIs whose behavior was changed; need to make sure it is up-to-date.
For example this one.
Microsoft.PowerShell.DesiredStateConfiguration.Internal.DscClassCache class
https://docs.microsoft.com/en-us/dotnet/api/microsoft.powershell.desiredstateconfiguration.internal.dscclasscache?view=powershellsdk-7.0.0

However this looks like auto-generated from XML comments in source code.