To list all users, use mongosh to query the system.users collection:
Before You Begin
Starting in MongoDB 8.0, you can use the directShardOperations role to perform maintenance operations that require you to execute commands directly against a shard.
Warning
Running commands using the directShardOperations role can cause your cluster to stop working correctly and may cause data corruption. Only use the directShardOperations role for maintenance purposes or under the guidance of MongoDB support. Once you are done performing maintenance operations, stop using the directShardOperations role.
Steps
use admin db.system.users.find()
Important
Do not modify the system.users collection directly. To manage users, use the designated user management commands.
To list all users of a sharded cluster that were created through a mongos, connect to a mongos and run the preceding command. MongoDB stores users that are created through a mongos in the admin database of the config servers.
To list all shard local users, connect to the respective shard directly and run the preceding command. MongoDB stores shard local users in the admin database of the shard itself. These shard local users are independent from the users added to the sharded cluster through a mongos. Shard local users are local to the shard and are inaccessible to mongos.