Since the first day of this year, eBay Bucks can not be used to purchase eBay gift cards. This new rule is still in effect. You can see the full terms for eBay Bucks here. But it looks like for now you can purchase eBay gift cards with eBay Bucks, if you go through the eBay app.
This is most likely a glitch that will be fixed soon. But if you want to use your first quarter eBay Bucks before they expire, this is a great way to extend their life. eBay Bucks will expire on May 2nd (they usually expire about a month after being issued), but eBay gift cards never expire.
Search for eBay gift cards in the app, and add add your preferred denomination from these cards sold by PayPal Digital Gifts. Check eBay Bucks and if it gives you an error, just try again.
Let me know if it works for you.