A buyer compares before buying, and what they compare is the name, the picture, the price and whether it is in stock. This is what one listing needs, and what kinds of thing may be listed.
Four fields, written once, that save you the questions afterwards.
Size, colour, language, capacity - they are axes on one product: the buyer picks from a single page, your stock stays in one place, and four copies of the same thing stop competing with each other for the same slot.
Each variant carries its own price, stock, picture and barcode if you want them, and can carry its own offer - or inherit the product's, whole.
A physical product that ships, a digital one whose link is released after payment, a box that gathers several items under one price, a wholesale line priced from a quantity up, a laundry service, or a service inside an event.
Each has its own form and its own fields in the panel. The main category is what decides where a product appears and what rate it is charged at - one product under exactly one category.
Listing happens in the panel, and there is no cap on how many.