You could have just said "Ryanair" and that's all the description you need. Ryanair is designed by assholes. They deliberately designed every element of their business to squeeze pennies out of you for services other airlines offer for no cost at all. And they seem in no rush to tell you about these things until the last possible moment, just so they can catch you off guard and add a last minute charge.
AssholeDesign
This is a community for designs specifically crafted to make the experience worse for the user. This can be due to greed, apathy, laziness or just downright scumbaggery.
It's Ryanair, this is nothing.
For every decision they take they always consult the Big Encyclopedia of Dark Patterns and Asshole Design™ to maximize the damage to the user
Probably they noticed that a virtual gift card will get used very soon (example give the money for a trip to someone else) so they are going to charge extra for the "convenience" while the physical because arrives weeks later via snail mail gets forgotten and they can keep the unused credit at expiration.
"Welcome to Ryanair! As a forward thinking company, we have added a hoop for you to jump through for your convenience! Only £5 per jump! ...Oh, no, the only way to board the plane is to use the hoop. But for an additional fee, we will extinguish the fire before you jump!"
They should put the gift card through a scanner and send the image. If it's that easy, charging for it is asshole-ish for sure.