Hi Sabrina, the Woocommerce light box effect has been moved to the theme since Woocommerce version 3 I believe. This is no longer a setting in Woocommerce but may appear as an option in your theme settings. Or not, it depends on the theme…
In Easy FancyBox Pro, the second “Apply to” setting “Links inside Sections” is meant to be able to control in which parts of your pages the FancyBox light box effect should occur. This option must be used in combination with the Senction(s) field that appears a little lower on the page.
In that field, you can set up some identifiers like div classes or IDs that are part of your theme. The plugin will then look for these on each page load and behave accordingly.
This means that it all depends on your theme what should be put there.
If you can share a link, I can take a look and try to figure out what is needed to get the result you want. You can use the contact form on this site if you prefer to keep the site address private.