SQL Server 2019 Core - Always on Availability Group - Availability replica is disconnected
I just figured it out.

(You have to have the [Domain\sqlengine] added to the Logins for SSMS.)

In Management Studio
Click [Logins]

Perform the following (2) actions


  Action #1
  Double Click [Domain\sqlengine] Click on [Server Roles] (I
  have the following checked, I actually had them all checked for
  testing, and now these are the ones that are needed.)
  dbcreator
  public (default cannot uncheck this)
  serveradmin
  sysadmin   


(This is what did the trick, this is what I was missing.) 


  Action #2
  Click on [User Mapping]
  Put a check on [Master]   


Click [OK]
Then Re-run the Always On Wizard   

This is all it took.
For the last few days.
I have been banging my head against the wall to get this working.
And it was right here all along.  

Hope this will help someone out.  

Wayne