As much as I understand there is no such functionality in grav yet.
If I do it like this, and provide a [email protected], always the "1x" version is used
---html
<div class="hero-image" style="background-image:url( {{ page.media['hero.jpg'].url }} )"></div>
TXT
I'm not a CSS expert but it looks like image-set is the equivalent to srcset for background images. Unfortunately image-set is not well supported by browsers at this time.
Any ideas or plans to achieve this? Thx