Microsoft Virtual Academy
MS Documentation has 3 or 4 different versions or places to keep the technical information on almost all of its mainstream products. The newest or most updated should be this one DOCS, which they call it modern experience.
In the meantime, MS also keep updating other two legacy document repositories – TechNet and MSDN. For example, on the topic of Windows Server, they have:
Of course, from time to time, they put redirection gradually to the new Docs platform – for Windows Server, TechNet link now points to Docs already, MSDN doesn’t have update on Windows Server 2016. So you can look around for more information, or just stick to Docs for the newest.
One more thing, MS also has presence on Git, so similar topic has some overlap documentations there.
This is a MVA link to a number of free Microsoft Press books, but it hasn’t been updated since a year ago, kind of outdated: https://mva.microsoft.com/ebooks.
I would recommend this link from Eric Ligman, updated every summer, huge number of books, there is even a PowerShell script that you can download them all at once: https://blogs.msdn.microsoft.com/mssmallbiz/2017/07/11/largest-free-microsoft-ebook-giveaway-im-giving-away-millions-of-free-microsoft-ebooks-again-including-windows-10-office-365-office-2016-power-bi-azure-windows-8-1-office-2013-sharepo/
This site has quite a few rich format content regarding SharePoint: