List all Orphan users in a SQL Server database

CREATE TABLE ##ORPHANUSER (
DBNAME VARCHAR(100)
,USERNAME VARCHAR(100)
,CREATEDATE VARCHAR(100)
,USERTYPE VARCHAR(100)
)
EXEC SP_MSFOREACHDB ' USE [?]
INSERT INTO ##ORPHANUSER
SELECT DB_NAME() DBNAME, NAME,CREATEDATE,
(CASE 
WHEN ISNTGROUP = 0 AND ISNTUSER = 0 THEN ''SQL LOGIN''
WHEN ISNTGROUP = 1 THEN ''NT GROUP''
WHEN ISNTGROUP = 0 AND ISNTUSER = 1 THEN ''NT LOGIN''
END) [LOGIN TYPE] FROM sys.sysusers
WHERE SID IS NOT NULL AND SID <> 0X0 AND ISLOGIN =1 AND
SID NOT IN (SELECT SID FROM sys.syslogins)'
SELECT *
FROM ##ORPHANUSER
DROP TABLE ##ORPHANUSER

Preventing logins and users to see metadata in SQL Server

To hide databases to all LOGINS, remove/revoke "VIEW ANY DATABASE" permission from the public server role

USE master;
GO

REVOKE VIEW ANY DATABASE
 TO PUBLIC;

To allow only some logins to view all databases, Jus create a user-defined server role

USE master;

CREATE SERVER ROLE [DBViewer];
GO

GRANT VIEW ANY DATABASE
 TO [DBViewer];

ALTER SERVER ROLE [DBViewer] ADD MEMBER [MyLogin];

This code creates a server role named DBViewer and grants the
VIEW ANY DATABASE permission to it. It then adds the login MyLogin to it.

Note: MASTER and TEMPDB will always be visible to all logins,We cannot make them invisible.

Script to sync up logins and database users in SQL Server

USE DATABASE
GO

EXEC sp_change_users_login 'update_one'
 ,'databse username'
 ,'loginname'
GO

Script to find number of users connected to SQL Server

SELECT COUNT(*) AS ConnectionCount
FROM sys.dm_exec_sessions
WHERE is_user_process = 1

Change the ownership of SQL Server agent jobs

The jobs may start failing when their AD accounts are removed. If the users have left it is better to change the job owner to a different account.
To ensure such issues wont happen, it is better to create a generic AD account with only necessary permissions and use it exclusively for this purpose.

List down all the jobs which are tied to the users and share it with all the respective project managers and technical architects and get a approval .
Decide on a common user account and create new one .