CF for Contact Form 7, bootstrap, modal, Contact Form 7

You need to initialise the form when the popup opens.

More information here: https://conditional-fields-cf7.bdwm.be/popup-test/

Given that you are following the example code on https://getbootstrap.com/docs/4.0/components/modal/

this should do the trick:

$('#exampleModal').on('show.bs.modal', function (event) {

  const $form = $(this).find('.wpcf7-form').eq(0);

  // register all the necessary events on the Contact Form 7 form
  wpcf7.init($form[0]);
    
  // register all the necessary events for the conditional logic to work
  wpcf7cf.initForm($form);
})