Metaversal on three.js project - is the transparent background available?

I am creating a content to use in Meta Quest3, by using three.js framework.

I’ve found that I can see the real-world background in this A-Frame portal sample when opening in Meta Quest 3 browser,

but my project, as same as another three.js sample such as below, only shows the black background like a VR content.

Is there any way to enable real world background in the three.js projects as well as the A-Frame projects? Thank you!