How to fix DAG creation error in Exchange 2019?

Question

Mail server

Background
There are two Exchange 2013 servers in the DAG. They work, everything is
fine. We have implemented two more Exchange 2019 servers. We want to gradually migrate the current mailboxes from the old servers to the new ones.
To do this, we are trying to create a separate DAG on these servers, so that you can create databases there and then start the migration

. I do everything according to the instructions from the MS website.
1. I set up a witness server (I add a user (Exchange Trusted Subsystem to the local admins group)
2. I create a DAG
And then an error occurs all the time. I just can’t add the server to the DAG group.


The server is either not added, or added, but the DAG does not function normally. An IP address is not assigned.
Launched the cluster test, writes that the witness server is not configured. But on the witness server itself, the user has been added to the Admins group. Catalogs and balls are automatically created.

There is a theory (because for some reason the log is written to the old EX servers) that the problem is that we have heterogeneous servers and as long as there are EX2013 servers on the network, we will not overcome this problem. But I would like to be 100500% sure. Because if I can't create a DAG after moving boxes and deleting old servers, it will be very bad.
Basically, I need your advice.

UPD. New input.
Through reboot and some mother, I managed to add all the servers to the DAG. Moreover, there were no errors.
and here's where it gets more interesting.

1. If you make a Get-MailboxDatabaseCopyStatus request, then the databases in this new DAG have the status ContentIndexState - NotApplicable


2. If you go to the cluster snap-in, it says that the witness server is not configured.
We did everything according to the instructions from the MS website. On the witness server, the Exchange Trusted System user has been added to the local admins. When creating a cluster, the witness directory was created, there is a ball.

Answer 1

In general, I did not find what the problem is.
The point is. DAG is not created with an IP address
The cluster itself is created, but when you try to add hosts to it, either an error occurs or there is no quorum. IP is not pinged. Tried everything, nothing helped.
As a result, I made a DAG - without IP. Microsoft even recommends doing so. Allegedly, the old version of the cluster is outdated and blablabla ...
Everything took off with a bang. The cluster is running. It is a pity that not as we would like, but the main thing is that it works.