I am new to AWS. I have seen numerous definitive answers saying Windows and AWS EFS can't work with each other. Is it still the case with Windows Server 2016?
Yes they can but it's some work.
Amazon clearly states that EFS + Windows is not supported. But that doesn't mean it isn't possible. CITI @ University of Michigan made an NFSv4.1 client for Windows several years ago.
To use it with AWS EFS you have to comment out one definition so that it always uses OPEN4_SHARE_DENY_NONE for the share-deny value – AWS specifically states in its Unsupported Features page as disallowing any other value.
And then compile, sign and install. It's not a trivial process, but it's doable. I'm running EFS + Windows Server 2012 R2 on EC2.
More detail in an answer to a similar question: https://stackoverflow.com/a/46625030/137641