checkout
Disable Coupon in Magento2 in the cart and in the checkout
The best approche is to add these files "checkout_cart_index.xml" and "checkout_index_index.xml" in this directory
app/design/frontend/{Vendor}/{theme}/Magento_Checkout/layout/
with this content
checkout_cart_index.xml
Magento2 Hide Discount Code form Cart and Checkout Page
the best way is to work on your custom theme by modifying these files
/app/design/frontend/{Vendor}/{theme}/Magento_Checkout/layout/checkout_index_index.xml