Hello Alexandre,
I tried yesterday, for experimental reasons, exact the way described in the migration documentation. It works as expected and all packages are available:
-
UiPath.Workflow at
https://www.nuget.org/packages/UiPath.Workflow -
UiPath.Workflow.Runtime at
https://www.nuget.org/packages/UiPath.Workflow.Runtime -
System.Activities.Core.Presentation and System.Activities.Metadata
If I see it correctly this is a UiPath specific portation of the dotNET framework assembly (many thanks to the UiPath development team for this great work
). You can find it in your Studio installation, e.g. %USERPROFILE%\AppData\Local\Programs\UiPath\Studio. Not in a public repository, but available 
.
Best regards
Stefan