Not need customize site.php. Enough custom css code.
Set image overlay as transparent.
Add this class in image addon whole-image-clickable.
Add this code in template custom.css file.
.whole-image-clickable .sppb-addon-image-overlay-icon {
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 100%;
border-radius: 0;
font-size: 0;
margin: 0;
background: rgba(0, 0, 0, 0.3);
}
To add font awesome icon use this code
.whole-image-clickable .sppb-addon-image-overlay-icon::before {
content: "\f00e";
position: absolute;
font-family: 'Font Awesome 5 Free';
font-weight: 900;
font-size: 50px;
top: 50%;
left: 50%;
transform: translate(-50%, -50%);
color: #fff;
}
It will looks like this