You can do this directly from Apple’s Photos. If possible format the SSD or the USB-stick using APFS. Create a folder named
DCIM in the root level on it (this will facilitate the input on the iPP4). Connect the USB-SSD or stick. Open Apple’s Photos, select the images, tap the
Share
-icon, choose
Save to Files
and then select the connected SSD/USB-C stick via the dialogue.
For the amount of time it takes, if possible, do not use a spinning HD.
Apple’s Files is occasionally prone to “silly” behaviour or errors: to preemptively avoid some of that, make sure the SSD/stick is formated APFS and copy in batches. Check whether the images are damaged after copying from the iPP3 to the SSD/stick before putting them on the iPP4.
If you connect the SSD/stick with the images inside the
DCIM folder to the iPP4 and open Apple’s Photos, the drive can be selected in its sidebar like e.g. most digital cameras and you then just import.
IMHO you should use
FileBrowser in whatever incarnation for the transfer from the older iPP3 - besides a more stable interfacing with external media (besides various other functionality), it allows to copy directly out of the Photos library and it is far less prone to errors compared to Apple’s Files.