hi @andrasetof30 ... I'm using the following code to only allow users to select a date from today, out 60 days... in my example below, my calendar is actually part of a gallery (which is why I'm referring to the selected date as ThisItem.Value)... but you can replace that reference with the name of your date picker (datepicker.selecteddate)...
i know this isnt exactly the logic you're looking for, but hopefully this can give you a reference you can adjust for your scenario?
If(
Date(Year(ThisItem.Value), Month(ThisItem.Value), Day(ThisItem.Value)) >= DateValue(Now()) And
Date(Year(ThisItem.Value), Month(ThisItem.Value), Day(ThisItem.Value)) <= DateAdd(Now(), 60, Days),
< acceptable date logic goes here >,
Notify("Only dates between " & DateValue(Now()) & " and " & DateAdd(Now(), 60, Days) & " will be accepted.", NotificationType.Error, 2000)
)