Putting the 2019 server into the existing 2012 cluster – as expected, this fails due to the operating systems being different

Attempted to just add it to the existing AGs when not being in a cluster – this fails because it’s not in a cluster

Created a separate single node cluster for the 2019 server and attempted to add as a replica to the AGs – this fails as well

Evict it from the existing 2012 cluster

Rebuild it with the Windows Server 2019

Create a new WSFC with one node

Install SQL Server 2017 …