Externe Festplatte

Do not export any images. Exporting is an 'export and forget' option, so Lightroom Classic will not remember what it did export. Here's how to do this. Copy the folders from the three disks to the new disk, using the Macintosh Finder, not Lightroom. Then in Lightroom, right-click on a top folder of one of the three old disks, and choose 'Update Folder Location'. In the dialog that comes up, navigate to the same folder on the new disk and select it. That will 'reconnect' this folder and all its subfolders to the new disk. Repeat this with the other two disks, and with any other top folder if you have more than one top folder per disk.

P.S. You can also reconnect the folders while the three old disks are no longer connected to your computer (because of lack of ports, perhaps). The only difference will be that Lightroom will show all the old folders as 'missing', and the menu is not 'Update Folder Location', but 'Find Missing Folder'. Everything else is the same.