Installed 21R1-Mart-Build-1590 and DM21R1-Refresh-Build-19986. They both installed successfully but there are two issues:

1) Trying to connect to MartServer from the DM client, get the following error "The client application version is different from Mart Server version. Install the same version of the application and the Mart Server and then try"

2) Trying to login to the Mart Administrator it seems underscore character "_" is not allowed as the user name. While on 2018R1, our admin username was as an example erwin_admin. Entering erwin_admin  in Username on 2021R1 Erwin Mart Administrator, after entering the underscore character the Username box  gets highlighted with a "Enter valid username" msg.

Thanks.