Hi, as I remember using extra custom CSS should be possible.

But anytime you can customize addon code and add needed features.

BTW

Check also Image Layout addon.

Hi.

But how and where, appropriate modifications should be made? I am committed to achieving such an effect: https://obst.pl/

Regards

Have you seen CSS code that they used, it was quite simple, you can use similar as webmaster. I mean text with link inside should fill whole box. You can try with Raw HTML addon.

BTW

In Image Overlay addon you can use link for title

but I think the simplest option will be just a simple customizaton of tht addon code (site.php) to add link < a href="/... taken from Button before class sppb-addon-overlay-image-content.