The “Interpolate” checkbox in Volumes module’s Display section only affects how that particular node is visualized. It does not affect how that volume is processed, segmented, etc. It does not affect any other nodes, e.g., a segmentation node that it is used with.
If the input volume’s resolution is too low to represent all the details you want to segment then you can use “Crop volume” module before segmentation to resample the volume at a finer grid with interpolation (and usually you also want to reduce the extents of the volume to the minimum size, to improve processing speed). Alternatively, you can keep the original volume intact and oversample the segmentation by using the segmentation geometry button on the right side of the master volume node selector in Segment Editor module.
