Hello Power_Jin, and welcome to the Unreal community.
Your concern relating to the blurriness of the Quixel nanite meshes may well have to do with the import settings. Please right click your texture samples and select convert to regular texture. As noted by member EnjuY1517, if this does not alleviate the concern you may have exceeded your texture streaming pool size. EnjuY1517 continues with their answer on how to increase the value.
Quixel assets are never going to have any more detail than the high poly source mesh. If you feel like something is off, compare what you’re seeing in UE5 to the source mesh opened in another application. You can also turn off Nanite in UE5 and see how the asset looks before Nanite modifies the mesh.
Quixel assets tend to be a few million tris at most, so that holds up extremely well with small assets like induvial rocks, but really starts to break down when it’s a giant patch of ground or an entire cliff.