catalog copy from external drive - no previews shown....

hi
i copied my lightroom catalogue to an expernal encrypted usb-drive. I can’t open it directly on the external drive (because it is read-only) so i copied it on my notebook (windows).
When i open it in Lightroom it updates the catalog (which works fine) and then opens it …. unfortunately not a single preview is shown although i also copied those files with the catalogue
(yes, i did not take all original photos with me as i intended to do most work in the catalogue section (where the previews would be enough to have).
can i somehow get those previews to be shown in the catalogue?