Who is connected, to which database, from where. Uses sys.dm_exec_sessions, which replaces the old sys.sysprocesses view. Works on SQL Server 2016 to 2022 and later.

-- Connections per database and login (SQL Server 2016-2022)
SELECT DB_NAME(s.database_id) AS [Database Name],
       s.login_name           AS [Login Name],
       s.host_name            AS [Host Name],
       s.program_name         AS [Program Name],
       COUNT(*)               AS [No Of Connections]
FROM sys.dm_exec_sessions AS s
WHERE s.is_user_process = 1
GROUP BY s.database_id, s.login_name, s.host_name, s.program_name
ORDER BY [No Of Connections] DESC;