USE [master]
    IF NOT EXISTS
    (SELECT name
     FROM master.sys.server_principals
     WHERE name = 'Domain/Login')
BEGIN
    CREATE LOGIN [Domain/Login] FROM WINDOWS WITH DEFAULT_DATABASE=[master]
END

SET NOCOUNT ON
DECLARE @user_to_be_added sysname
DECLARE @sqltext nvarchar(max) = N''

-- change below to your user to be added .. make sure that the login is already existing
    SET @user_to_be_added = 'Domain/Login'
SELECT  @sqltext += char(10)+ 'use '+quotename(name)+';'+char(10)+ 'CREATE USER '+quotename(@user_to_be_added)+' FOR LOGIN '+quotename(@user_to_be_added)
FROM sys.databases where state_desc ='ONLINE' AND databaseproperty(name,'isReadOnly') = 0

SELECT @sqltext

--- once above looks good with the output uncomment below line
    --EXEC sp_executesql @sqltext;

SpConfigure
CustomErrors
Credentials
DatabaseMail
LinkedServers
Logins
LoginPermissions
SystemTriggers
DatabaseOwner
AgentCategory
AgentOperator
AgentAlert
AgentProxy
AgentSchedule
AgentJob

SET NOCOUNT ON
DECLARE @user_to_be_added sysname
DECLARE @sqltext nvarchar(max) = N''

-- change below to your user to be added .. make sure that the login is already existing
SET @user_to_be_added = 'Domain/Login'
SELECT  @sqltext += char(10)+ 'use '+quotename(name)+';'+char(10)+ 'CREATE USER '+quotename(@user_to_be_added)+' FOR LOGIN '+quotename(@user_to_be_added)
FROM sys.dm_hadr_availability_replica_states ars
inner join sys.databases dbs ON ars.replica_id = dbs.replica_id
 where dbs.state_desc ='ONLINE' AND databaseproperty(dbs.name,'isReadOnly') = 0
and ars.role_desc = 'PRIMARY' -- we want to filter only Primary AG where dbs are writable.

 if  (@sqltext <> '')
 begin
  select @sqltext
  end
  else
    begin
    print 'There is nothing to print - @sqltext is blank'
    end