function product_designer_fonts_custom_20200808($fonts){

$fonts[] = array('name'=>'Rye');
$fonts[] = array('name'=>'Nosifer');

return $fonts;
}

add_filter('product_designer_fonts', 'product_designer_fonts_custom_20200808');

Removing existing fonts

function product_designer_fonts_custom_20200808($fonts){

    // to remove existing fonts just replace the variable($fonts) name with new variable($my_fonts)
    
    // adding Google fonts
    $my_fonts[] = array('name'=>'Rye');
    $my_fonts[] = array('name'=>'Nosifer');

    // Adding custom fonts
    $my_fonts[] = array('name'=>'myFirstFont', 'src'=>'http://www.w3schools.com/cssref/sansation_light.woff');


    return $my_fonts;
}
add_filter('product_designer_fonts', 'product_designer_fonts_custom_20200808');