You also need to stop client traffic to the servers
Follow this, it applies to 2019 as well
https://practical365.com/exchange-server/installing-cumulative-updates-on-exchange-server-2016/
This browser is no longer supported.
Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support.
Is it really just as simple as login in to Exchange Admin Center and do the Server Switchover to make the one I don't want to upgrade the target server so that all the mailboxes are primary on the other server and then run my updates and then after that one is done switch over to the other server? Is it more complicated than that? Do I need to stop any services? Is there anything else I need to do. I am having a hard time trying to find specific instructions when running a 2 member DAG for Exchange Server 2019 so I just want to be sure I don't leave anything out.
You also need to stop client traffic to the servers
Follow this, it applies to 2019 as well
https://practical365.com/exchange-server/installing-cumulative-updates-on-exchange-server-2016/