As mentioned in this thread, you’ll need to use the 2025-04 Admin API in order to create a discount node of that type.
If you create a deprecated dedicated discount/product/shipping discount function, then those are compatible with the < 2025-04 Admin API when creating the discount node.
My solution was to only use the 2025-05 when creating the discount node, until I’m ready to upgrade the rest of my app.