I was talking to someone recently about online training courses from Microsoft and directed them to the Microsoft Virtual Academy which I looked at quite a while ago now.
However, they came back to me to let me know that it is being retired in favour of Microsoft Learn.
Microsoft Learn seems to be mainly focused on Azure with a few courses available for PowerBI, Power Apps and Flow.
The documentation for Microsoft Dynamics GP is being added to the Microsoft Docs libary. Some of the documentation is already there and Microsoft have announced that more will be added through time. Hopefully, this will be accompanied by the documentation being brought up-to-date as much of it has not been updated since Dynamics GP 2013.
Microsoft have also opened the documentation for contribution by the community. The documentation is available for contribution via a public GitHub repo.