Users is your system

Question: Hello, what is the transaction/report, if any, to find what users have been created in your SAP system ?

Answer:
There are lots.

Tables USR01 or USR02
Transaction SU01

Have a look around the user & roles infosystem in the standard menu

Answer:
Go to SE16 transaction and run the report, v_username.
This will give u the list of users present.

Answer:
Go to SE16 transaction and run the report, v_username.
This will give u the list of users present.
Technically it's a view, not a report.

Answer:
Whatever it is, it should solve the problem