search for a person on a external hard disk

Can you clarify which program you are using? If the images of that special person that are stored on the external drive have been imported into either of the two different Lightroom versions, then it should be possible to search for a specific person in the Lightroom catalog. However, subsequently locating the images of that specific person in Lightroom requires that the specific person has somehow been previously identified to Lightroom, either by using the face recognition feature or by adding a suitable identifying keyword tag.

If the images on the external drive have NOT been imported into Lightroom, then you cannot use Lightroom to locate them.