If you want to splurge on a gift, consider giving your artist a new iPad.
They're available in a variety of price points that reflect the size and storage. More storage is always better, but you can also pay a few dollars per month for extra cloud storage.
Unless they are really serious with their art, it's probably not necessary to buy the Pro version. It is a bit faster and allows the user to add more layers, but I haven't noticed any significant difference in mine.
If they're new to drawing with Procreate, consider getting them a subscription to Skillshare. I've been a member for years now and I still love it. Skillshare has taught me almost everything I know about graphic design.
Skillshare is a learning platform that has classes on Procreate, drawing, painting, graphic design, and more. New classes are added all time by some of the best artists in the industry.
Procreate brushes can help create really unique art. You can get them to add textures, patterns, and more. The one I linked is one of my favorite sets. It lets you add body templates to create characters. This is great for people like me who want to draw people, but don't know where to start.
Creative Market also allows you to buy credits or their new membership program that allows you to download a certain amount of items per month.