Get instance of Swiper from DOM

swiper.js

// This example shows us how to update broken swiper after Fancybox carousel closing
if (typeof fancyboxInit !== undefined) {
  // Main approach here is the next row  
  $.fancybox.defaults.backFocus = false;
  let showCaseSlider = $('.showCaseSlider .swiper-container');
  $('[data-fancybox]').fancybox({
    afterClose: function() {
      if (showCaseSlider) {
        let showCaseSliderInstance = showCaseSlider[0].swiper;
        showCaseSliderInstance.update();
      }
    }
  });
}

Thanks for the advice @ImKubass