You can check for category slug or id, and filter woocommerce_is_purchasable like so:
function BN_restrict_store_only( $purchasable, $product ){
//The category by slug
$pickup_prod_cat_slug = 'available-in-store-only'; // slug
//The category by id
$pickup_prod_cat_ids ='681'; // the id of the product cat
// For variations (
if ( $product->is_type('variation') ) {
$parent = wc_get_product( $product->get_parent_id() );
$product_id = $parent->get_id();
if ( has_term ( array( $pickup_prod_cat_slug, $pickup_prod_cat_ids), 'product_cat', $product_id )) {
$purchasable = false;
}
}
// For simple and other product types
else {
$product_id = $product->get_id();
if ( has_term ( array( $pickup_prod_cat_slug, $pickup_prod_cat_ids), 'product_cat', $product_id )) {
$purchasable = false;
}
}
return $purchasable;
}
add_filter( 'woocommerce_is_purchasable', 'BN_restrict_store_only', 10, 2 );
add_filter( 'woocommerce_variation_is_purchasable', 'BN_restrict_store_only', 10, 2 );
Works both with simple products and variations.
You have to make a category with the slug "available-in-store-only" or get the id/slug of whatever product cat you want to use.
File goes in the functions.php of your child theme, or CodeSnippets.