Here is your microflow:
and focused on the xpath of the retrieve:
You need addMonths or addMonthsUTC, depending if your date is localized or not. Something like the expression below:
addMonths([%CurrentDateTime%], 3) <= [%CurrentDateTime%]
The documentation below may help:
https://docs.mendix.com/refguide/add-date-function-calls/#addMonths
You are almost there. Try this one:
$Personnel/Enddate >= [%BeginOfCurrentDayUTC%] and $Personnel/Enddate <= addMonths([%EndOfCurrentDayUTC%],3)
Regards,
Ronald