Set To Date with Custom Format

Force the To date value based on the From selected date, adding extra days and managing the custom format

Custom Script

Add an HTML Widget BEFORE the Form with this custom script to manage a personalized “” date format

    function format_date(date) {
    let tmp = date.split('.');
    date = tmp[2]+'-'+tmp[1]+'-'+tmp[0];
    let current_date = new Date(date);
    let days = 5; // change with your days
    current_date = new Date( current_date.getTime()+(days*24*60*60*1000) ); 
    return ("0" + current_date.getDate()).slice(-2) + "." + ("0" + (current_date.getMonth() + 1)).slice(-2)
 + "." + current_date.getFullYear()

NOTE: If no custom Date Format is forced you can use a single line solution directly into the Set Value field:

new Date( new Date([field id="from"]).getTime()+(5*24*60*60*1000)).toISOString().split('T')[0]

Set Value

Add this rule on Fields Conditions with Value:

=format_date([field id="from"])