You can achieve that using X Lightbox feature.
Create a page > ON WP Classic backend editor > under the blue update button > page attributes > page templates > select BLANK NO CONTAINER NO HEADER NO FOOTER
This will be your page which will be opened in a lightbox.
In the page you want to add the lightbox, you will add a raw code element and add lightbox selector, for example :
After that you will add a button or image or link and add a class to it:
You will link that to the page you previously created.
Let us know how it goes!