Code for multiple databases

DECLARE @Domain nVARCHAR(MAX) = 'icon'
DECLARE @User nVARCHAR(MAX) = 'synsdtnonprod'

-- Create the login and grant it sysadmin server role
EXEC ('USE [master]; CREATE LOGIN ['+@Domain+'\'+@User+'] FROM WINDOWS WITH DEFAULT_DATABASE=[master]')
EXEC ('USE [master]; ALTER SERVER ROLE [sysadmin] ADD MEMBER ['+@Domain+'\'+@User+']')

-- Get a list of all databases
DECLARE @Databases TABLE (DatabaseName nVARCHAR(MAX));
INSERT INTO @Databases (DatabaseName)
SELECT name
FROM sys.databases;

-- Loop through each database
DECLARE @Database nVARCHAR(MAX);
WHILE EXISTS (SELECT 1 FROM @Databases)
BEGIN
    SELECT TOP 1 @Database = DatabaseName FROM @Databases;

    -- Create the user in the current database and grant db_owner role
    BEGIN TRY
        EXEC ('USE [' + @Database + ']; CREATE USER ['+@Domain+'\'+@User+'] FOR LOGIN ['+@Domain+'\'+@User+']')
        EXEC ('USE [' + @Database + ']; ALTER ROLE [db_owner] ADD MEMBER ['+@Domain+'\'+@User+']')
    END TRY
    BEGIN CATCH
        -- Handle any errors, e.g., print an error message
        PRINT 'Error creating user in database ' + @Database + ': ' + ERROR_MESSAGE();
    END CATCH

    -- Remove the processed database from the list
    DELETE TOP (1) FROM @Databases;
END

-- Grant permissions in msdb
EXEC ('USE [msdb]; CREATE USER ['+@Domain+'\'+@User+'] FOR LOGIN ['+@Domain+'\'+@User+']')
EXEC ('USE [msdb]; ALTER ROLE [db_owner] ADD MEMBER ['+@Domain+'\'+@User+']')