The 1st image shows an imported object from ZBrush with a displacement map, which displays a detailed surface.

The 2nd image shows the object after vdbfrompolygons nodes are added, and the detail is gone.

Why is this happening, and what setting can I change to bring back the detail?

Thanks
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likely because you don't have UVs on the remeshed geo since displacement map relies on that

you may have some luck with Labs UV Transfer to transfer vertex uv attribute from original geo to remeshed geo

or alternatively you can create new UVs and bake the new displacement map

tamte
likely because you don't have UVs on the remeshed geo since displacement map relies on that

you may have some luck with Labs UV Transfer to transfer vertex uv attribute from original geo to remeshed geo

or alternatively you can create new UVs and bake the new displacement map

Many thanks, I will give it a go.

I have tried increasing the Res/Voxel Size on the VDBfrompolygons but anything over 0.002 crashes my system

Attached is an example of the setup (VD.exr file reduced to 1024px from 4086px)

iso
I have tried increasing the Res/Voxel Size on the VDBfrompolygons but anything over 0.002 crashes my system

Attached is an example of the setup

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As tamte correctly pointed out, it's not the resolution, but the UVs.
Your original vertices had UV coordinates to which the material was bound. When you converted the geo to VDB and back to polygons, you created a completely new topology, new points and polygons that are in no way related to the old ones—neither quantity nor position. Therefore, all the original attributes disappeared. And you need to restore the UVs so the material fits where it was. But how do you do this? Obviously, since these are completely different and unrelated topologies, you need to project the new topology onto the old one and read the UVs there. Whether you do this with nodes, VEX, or whatever is irrelevant. You just need to decide how to project—by the nearest position, or by the normal, or something else. Obviously, the projection may not be very good. The second option is to recreate the UVs, manually or through some linear projection. Honestly, I don't know of any easy ways here. Depending on the geometry and topology, one or the other will be easier.
Volumes obviously make objects much coarser, and a clear understanding of when and why to use them is needed.

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Gaalvk
As tamte correctly pointed out, it's not the resolution, but the UVs.

Thanks for the detailed explanation. It makes sense. I shall experiment some more to find a solution.

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