WooCommerce, change “Add to Cart” to “Link to Product”, only for specific categories

You can just add another check within that filter – get the category of the product the filter is currently active on and compare it with the category you want to target.

add_filter( 'woocommerce_loop_add_to_cart_link', 'replace_loop_add_to_cart_button', 10, 2 );
function replace_loop_add_to_cart_button( $button, $product  ) {
    if( $product->is_type( 'variable' ) ) return $button;

    // array of slugs for the categories you want to target
    $target_categories = array('target_category_slug1', 'target_category_slug2'); // add more as needed

    foreach ($target_categories as $category) {
        // check if product has the category
        if ( has_term( $category, 'product_cat', $product->get_id() ) ) {
            $button_text = __( "Read More", "woocommerce" );
            return '<a class="button" href="' . $product->get_permalink() . '">' . $button_text . '</a>';
        }
    }

    // return default button if product doesn't belong to the target categories
    return $button;
}

You can replace the elements in the $target_categories with your target category slugs.
This will return the “Read More” text if the product belongs to that category array, or return the default button if it isn’t.