Please open the navigation point Products in the shop backend. Here you can see that next to the search function the filter "Aktive Angebote" (active offers) is preset. This means that only products for which there is already an active offer will be displayed.
Please select the "Inaktive Angebote" (inactive offers) filter to filter for products that you have created but do not yet offer. Alternatively, you can also display "Alle Angebote" (all offers).