The pdbedit command with the -L or --list flag can be used to list the user accounts that have been configured as Samba users.

pdbedit --list

Something like this should be returned

john.doe:1004:

The -v or --verbose flag can be used to display more details.

Unix username:        john.doe
NT username:
Account Flags:        [U          ]
User SID:             S-1-5-21-2499246942-1831745003-2102366678-1000
Primary Group SID:    S-1-5-21-2499246942-1831745003-2102366678-513
Full Name:
Home Directory:       \\server1\john.doe
HomeDir Drive:
Logon Script:
Profile Path:         \\server1\john.doe\profile
Domain:               server1
Account desc:
Workstations:
Munged dial:
Logon time:           0
Logoff time:          Wed, 06 Feb 2036 09:06:39 CST
Kickoff time:         Wed, 06 Feb 2036 09:06:39 CST
Password last set:    Mon, 31 May 2021 05:33:08 CDT
Password can change:  Mon, 31 May 2021 05:33:08 CDT
Password must change: never
Last bad password   : 0
Bad password count  : 0
Logon hours         : FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF