1. Import your artwork into XD - I'm designing in Illustrator and using the 'Import' function.
2. Next, select the object that's supposed to have a gradient stroke applied (e.g. grey border).
3. Right-click the object and choose 'Outline stroke'.
4. Then, right-click again and choose 'Ungroup'.
5. Select the object one more time and you can now apply a fill with a colour gradient.
Here's my workaround:
1. Import your artwork into XD - I'm designing in Illustrator and using the 'Import' function.
2. Next, select the object that's supposed to have a gradient stroke applied (e.g. grey border).
3. Right-click the object and choose 'Outline stroke'.
4. Then, right-click again and choose 'Ungroup'.
5. Select the object one more time and you can now apply a fill with a colour gradient.