There are two sides in MATNET to make double-sided materials, so how to create double-sided materials that can be recognized by the XPU in the new version of Karma Material Builder, thank you.

You have to manually do it using the ray-import backface feature.
more details here
https://www.sidefx.com/forum/topic/93315/ [www.sidefx.com]
https://www.sidefx.com/forum/topic/93315/#post-409092 [www.sidefx.com]