If I’m understanding you correctly, I think what you want is to use JQL to break down the number of “Session Start” (manually tracked) events by the number of unique users right? Same as this report: https://mixpanel.com/s/KAqol
If so, you can use the following JQL query - you’ll find that the JQL output and the report results will line up.
function main() {
return Events({
from_date: '2025-01-16',
to_date: '2025-01-23',
event_selectors: [{event: "Session Start"}]
})
.groupBy(["properties.$user_id"], mixpanel.reducer.count())
.map(function(row){
return {
$user_id: row.key[0],
num_of_session_start: row.value
}
})
} 
