Thank you for the screenshot showcasing the issue you are having. This is expected behavior if you have your shipping rate threshold set to a minimum dollar amount. The shipping rate availability is calculated on the cart total, after discount. The easiest solution would be adjusting that threshold so that customers are able to check out with the discount and free shipping.
Alternatively you can create a discount combo for free shipping + the 10% discount.
Is not expected at all, there is 0 ecommerces in the world that works like this.
A customer CANNOT end up paying more with a discount than without, it’s stupidity at its peak.
And what you are purposing are not solutions.
The solution is allow us to give free shipping on the price after discount.