Hank here from Shopify.
While this is something that is not native to the Shopify admin, there are certainly some apps out there that will allow you to stack discounts, or combine discounts. I will list some of them below for you to browse!
Those are just some apps, but there are more for you to view here. The majority of these will work on the cart page, but they will have the specifics on the individual app listings page. You can also reach out to the app developer directly for further queries about the app from the listings page also!
I hope this assists you with combining/stacking discount codes, but let me know if you have any further questions!
All the best,