Starting 1.18 version we have added a new Testimonial slider shortcode.

The testimonial shortcode can be added from the shortcodes list

All details need to be added in the form:

To add images, you need to upload the image in Admin-Media

Edit the image

Copy the image URL

Paste the image URL in the shortocode

You can make a Testimonial slider with the help of a shortcode

You need to add Testimonial shortcode for this to work

or add existing Testimonial shortcodes from the page with drag and drop

Live examples https://main.wpestatetheme.org/other-shortcodes/