What have lines done wrong to not be considered as a shape? :O

Would you mind adding the gradient option for lines as well?

In the meantime, one possible workaround :

(1) Use a blurred image as background to your slide,

(2) Add your shape, and/or text,

(3) Duplicate the background image. Blur it. Crop it.

And voila 😄

I've been trying to use boxes to show a transition within a timeline with Gradients. Unfortunately shapes do not have gradients, therefore please add this feature for more customization space!

And text please. :)