Hi Marko,
That’s doable as well, enable Quantity Dropdown and Fixed Quantity (and per product) sections.
Then in the product page, define a maximum of 500 (so the dropdown feature will work) and then enter 100,200,500 in Exact quantity allowed field (product page as well), and this should do it for you, like this page:
https://wpwhale.com/?product=dropdown-product
Let me know if this is not what you’re looking for.
Omar
