When the Nintendo Switch launched in early March, users discovered that they could not store their credit card information through the marketplace. But no longer will you have to re-enter your information for every purchase (or stack your digital wallet with extra funds), as Nintendo has enabled the ability to store credit card information.
As discovered by Nintendo Everything, you will now see the option to store these details when buying an eShop game. You can then see this information on your Account Information page when it's stored. Along with this, you now have the option to require or disable password entry when buying something when your credit card details are on file.
This new feature comes to the eShop without an update, instead arriving through the background. Nintendo's support site still says you can't store credit card info, so this new feature apparently only just rolled out very recently.