Migration using Always On Availability Group between different Servers (2016 To 2019) Issues.

Hello, I am new here, I have a SQL Server 2016 with Four servers and they are part of a cluster, I am trying to migrate all the databases in the Primary replica to a new server. I have provisioned two 2019 servers one will be my New Primary replica and the second to be my secondary server.

I have added these two new servers into the Availability replicas (Part of the cluster now) On one node in the new servers after adding it, I always get this " Database is not synchronizing & Data Loss " Even after removing the servers many times to readd again, I will get this error, also when I tried to access the database, I will always get database not accessible on both Servers. Is the best method to do the migration? why is there anyway the database can be accessible? 

Thank you.