Why an external SSD? Are you very low on storage on your iPad?
You can connect external drives or SD Cards to your iPad. Then browse the content with the Files.app, not with Photos. Connect external storage devices to iPad – Apple Support (UK)
You can export the photos from your library on your Mac to nested folders on an external drive to preserve the albums as folders. Then use the Files.app on your iPad to view them.
The syncing method described by Matti will be much more convenient, but the synced photos will be stored locally on your iPad and need storage. The syncing will reduce the size and resolution, and you will be able to view the photos, but you cannot edit them unless you create a copy and import it into the Photos Library. And you will not be able to delete the synced photos without syncing again. You could be stuck with synced photos taking up too much storage when travelling and away from your Mac.