How to build calendar view from text fields?

First of all, text field as a data field is not supported.

Have a look at the document below might help.

https://fivejars.com/blog/all-you-need-know-about-fullcalendar-view-module

Secondly, this is a support request issue.

Text field as the date field is not supported?
But on the module page it is written:

You need a long plain text field to present the RRULE string for recurring logic of an event. For example,
DTSTART:20200302T100000Z
EXDATE:20200309T100000Z
EXDATE:20200311T100000Z
RRULE:FREQ=WEEKLY;UNTIL=20200331T120000Z;INTERVAL=1;WKST=MO;BYDAY=MO,WE

Why EXDATE is writen twice?

Ok, i provide new long plain text field vith value from readme...

...and rebuild view

And… Nothing… Again.

You need to learn what “RRULE” means.

This is a free contribution module built and help by volunteers.

Any bug report and feature request is welcome, because they will help others in the Drupal community.

I am close this issue as it is obvious misunderstanding.

Ok, i did it without module.

Here is my workflow.

Text fields on node

I think, that it will works with date_recur fields.

View with hidden fields

Global: custom text field is rewritten in template views-view-field--NAME-OF-VIEW--block-1--nothing.html.twig:

{{ attach_library('symnews/fullcalendar') }}

<script>
    document.addEventListener('DOMContentLoaded', function() {
        var calendarEl = document.getElementById('calendar');

        // Function to calculate duration from DTSTART and DTEND
        function calculateDuration(dtstart, dtend) {
          var start = new Date(dtstart);
          var end = new Date(dtend);
          var durationInMs = end - start;
          var durationInHours = durationInMs / (1000 * 60 * 60);
          return durationInHours + ':00';
        }

        // Event details
        var dtstart = '{{ view.field.field_start_text_field.original_value }}';
        var dtend = '{{ view.field.field_end_text_field.original_value }}';
        var duration = calculateDuration(dtstart, dtend);
        var rrule = '{{ view.field.field_rrule_text_field.original_value }}';
        
        var calendarConfig = {
          firstDay: 1,
          headerToolbar: {
            right: 'dayGridMonth,timeGridWeek,timeGridDay',
            center: 'title',
            left: 'prevYear,prev,next,nextYear'
          },
          initialDate: dtstart,
          events: []
        };

        if (rrule) {          
          var rruleString = 'DTSTART:' + dtstart + '\nRRULE:' + rrule;
          calendarConfig.events.push({
            title: '{{ view.field.title.original_value }}',
            rrule: rruleString,              
            duration: duration // Use calculated duration
          });
        } else {          
          calendarConfig.events.push({
            title: '{{ view.field.title.original_value }}',
            start: dtstart,
            end: dtend,
            duration: duration // Use calculated duration
          });
        }

        var calendar = new FullCalendar.Calendar(calendarEl, calendarConfig);

        calendar.render();
    });
</script>

<div id='calendar'></div>

MYTHEME.libraries.yml:

fullcalendar:
  version: 1.x
  header: true
  js:                         
    https://unpkg.com/fullcalendar@5.11.5/main.min.js: {}   
    https://cdn.jsdelivr.net/npm/rrule@2.6.4/dist/es5/rrule.min.js: {}   
    https://cdn.jsdelivr.net/npm/@fullcalendar/rrule@5.11.5/main.global.min.js: {}
  css:
    theme:      
      https://unpkg.com/fullcalendar@5.11.5/main.min.css: {}

Result here:

https://planetallgaeu.de/timely-import/kurkonzert-im-kurpark-bad-wurzach

if node will not exist - it looks like: