Upgrade Exchange 2016 underline operation system

[alang1991]

I'm running 5 exchange 2016 on Windows2012R2 with one DAG in 2 sites. Since Windows2012R2 reached end of life, I have to upgrade Windows2012R2  to windows  server 2016. What is best route?

My thinking is to take 2 servers off DAG, remove database copy, upgrade OS to win2016. Create a new DAG, and start migrating mailboxes to new DAG. Do the same for remaining servers one at a time. 

Any advice is appreciated. 

PS: the server hardware doesn't support win2019 and above. win 2016 is only option.

[#2]

My advice is build new servers and migrate your mailboxes to the new server(s). There's no supported path to upgrade the OS of an existing Exchange server.