@jwatte thank you for continuing to give me advice.
The asset I am using is this:
Temperate Vegetation: Spruce Forest
https://www.fab.com/listings/f8044501-17a2-498f-b198-5f1bc71ee87a
And this is the screen shot of the shader( The whole thing is too large, so this screen shot is just a part of it):
[Original]
[Set to Unlit mode]
As you suggested, I connected the texture to the ‘emissive’ channel, and initially, the material preview showed the ideal color. However, after saving and checking in the viewport, the mesh disappeared again. And when I moved the camera quite far away, the mesh reappeared.
I thought something was off, so I checked the material again, and the material disappeared. Is this a bug in UE5, or do I need to change other settings on the mesh in addition to connecting the texture to the ‘emissive’ channel?