Hi @Qilafara,
I think this is a data set issue, you need to add two columns represently for StartDate and EndDate, and then create another recurrence flow to trigger everday and check if there is anyone on leave today.
Recurrence, triggers everydaye
Get Items,
Condition, if today is between StartDate and EndDate.
formatDateTime(utcNow(),'yyyy-MM-dd')
Note that select the StartDate and EndDate from the dynamic content of Get Items action, and put them represently on the left pane of the condition, write the above expression on the right pane of the condition.
Using the Or to combine two conditions.
If yes, send an email to manager