You’ll not be able to use Earbuds that use a Lightning connector with a USB-C equipped iPad.
Whilst some MFI-approved adapters exist that allow connection of a USB/USB-C cable or device to an iPad with a Lightning port (which includes an “active” interface converter), the reverse arrangement is not available. The adapter is not simply a wiring or physical plug conversion - but instead includes active electronics.
You would be best advised to use commonly available EarPods with a 3.5mm audio plug, with a USB-C to 3.5mm Headphone Jack Adapter:
https://store.apple.com/uk/xc/product/MU7E2ZM/A