Unable to connect to the Reporting Services instance through SSMS with windows authentication I am trying to connect to Reporting Services instance SSRS with SSMS so that I can update some of the parameters on display of remote errors and retention of execution log statistics.

I receive the error message:

The username or password is not valid or you do not have permission to access this server. (Microsoft.SqlServer.Management.UI.RSClient)

Server 2016 with SQL Server 2017.  My network account is an admin on the local server and I have no problem connecting to all DB's on the sql side.
Since you have access to the server i'd reccomend you log in and use Reporting Services Configuration Manager to change whatever settings you want. If you cant do it via config manager then you may need to edit the config files. 

From memory to access SSRS via SSMS requires permissions on the service. Not the database.