When a product is added to the admin panel but users can't add it to their cart, it's likely because the item is marked as "catalog" or "classified" instead of being available for sale. Essentially, these types of products are intended for display or informational purposes rather than for purchasing. So, users won't be able to add them to their cart because they're not meant to be sold through the online store.
Screenshots: https://prnt.sc/kG2hmBaaTqdX