Hey,
You will still need to Pause+Draing roles on node1, evict it from the cluster rebuild it with Windows Server 2019, install all roles and features and then add it back to the cluster. Might help:
https://www.starwindsoftware.com/blog/cluster-rolling-upgrade-from-windows-server-2012-r2-to-windows-server-2016
Cheers,
Alex Bykovskyi
StarWind Software
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