Yes, Shopify doesn't support fixed-price discounts by default. Even you try to set up a Buy X Get Y discount, the get option cannot support it.
I'm developing an app to set up something like this: you can take a look at my demo here: https://benny-test-store.myshopify.com/products/summer-shoe-sales
Merchants can fill in a simple form to generate a template like this. Let me know if you find it relevant to your case. I'm finding users to join Early Access.