Migration Exchange 2016 to 2019; still dependent on 2016

I recently migrated from exchange 2010 to exchange 2016.  there were some hickups but was successful.  then I migrated to Exchange 2019.  I moved everything, settings and mailboxes.  however I, when I turn off Exchange 2016, Outlook stops working.  Some errors are "can't find the infostore." Exchange is offline.

I thought it was autodiscover, but I'm not sure.  I have set it to NULL. waited a few days and turned off the 2016 server: same issue.  I set it to the new server. same issue.  Everything I do seems not work; there still a dependency on Exchange 2016 server. 

I don't know if this matters, but the internal domain ("Domain1"), what we use for log ins and active directory, is not the same as our email address (I'll call email domain "Domain2")  I don't know if this is causing the problem too.

Thoughts or suggestions are welcome.