In v$session the column last_call_et has value which tells us the last time (seconds) ago when the session performed any activity within the database.

select username, floor(last_call_et / 60) "Minutes", status
from v$session
where username is not null –– to ignore background process
order by last_call_et;

USERNAME Minutes STATUS
—————————— ———- ——–
SYS 0 ACTIVE
SCOTT 0 INACTIVE
SYSTEM 34 INACTIVE
..