It is a somewhat known issue that si(alarmon) will return 1 if it finds some other time triggered events, like calendar notifications, modes and routines (formely bixby routines) and timer (there's one mention found by searching for alarmon).
I'm running a Samsung S23+ with Android 13 (One UI 5.1). I'm not running any automation apps besides Modes and Routines. The si(alarmon) function is returning 1 for: alarms (as it should), scheduled routines and calendar events with notifications. In fact, not only it returns on, but it will also use the next scheduled time from any of these conditions and returning it for si(alarmd).
The only thing close to a solution I've found is in this reddit post; but it doesn't solve my problem.