Epidemic "User Name and Password incorrect"

Hello there, scenario: all OS Server 2019 Standard, all Exchange are 2019 with latest CU 15.02.1258.023. Machines involved in this case: 2 ADC, 3 Exchange, 1 Windows 11. All except one ADC report incorrect user name and password for Outlook, one Exchange Outlook additionally reports not to be able to extend folders. It looks like there is an interaction error btw. Outlook (or the new designation) and Exchange servers. The epidemit started in Win11 and covers now all mentioned systems except for one. The basic logon to EAC works but not EMS:

"VERBOSE: Connecting to [Servername] FQDN.
New-PSSession : [Servername] Connecting to remote server [Servername] failed with the following error message : The user name or password is incorrect. For more information, see the about_Remote_Troubleshooting Help topic.
At line:1 char:1
+ New-PSSession -ConnectionURI "$connectionUri" -ConfigurationName Micr ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : OpenError: (System.Manageme....RemoteRunspace:RemoteRunspace) [New-PSSession], PSRemotin
gTransportException
+ FullyQualifiedErrorId : LogonFailure,PSSessionOpenFailed

Have already tried many possibilities but none worked. With EMS (after unsuccessful logon) test-servicehealth and test-replicationhealth for ReplayService, ActiveManager and ServerLocationService work but get-mailboxdatabasecopystatus * | ft -auto reports service down for the remaining 2 Exchange. I'm really sorry for having to ask the community but have tried many attempts w/o success. Thanks a lot for any help, Marcel