How to view files from Portable SSD on MacBook

Is the device your Time Machine backup device?

See this on how to view the files in your Time Machine backup

1. On your Mac, open a Finder window, then type a search word or phrase in the search field in the upper-right corner.
2. Refine the results by specifying search criteria using the search bar.
3. Click the Time Machine icon  in the menu bar, then choose Browse Time Machine backups.
4. If the Time Machine icon isn’t in the menu bar, choose Apple menu  > System Settings. Click Control Centre in the sidebar, scroll down to Time Machine , then select “Show in Menu Bar” from the pull-down menu.
5. Use the arrows and timeline to browse the Time Machine backups.
6. Select one or more items you want to restore (these can include folders or your entire disk), then click Restore.
7. Restored items return to their original location. For example, if an item was in the Documents folder, it’s returned to the Documents folder.

See this link for further reference Recover files using Time Machine and Spotlight on Mac - Apple Support

Locate the photos (the folder that they are in) on that external drive. Or search by name/kind:image/file extension. Double-click. Does that not work?

For (local) photos from the Photos app, those are a bit special, as they’re in a managed database. The image name is different from the filename in the Photos Library.photoslibrary ‘package’. The photos in the library get randomized Finder names like BAE2491A-44FF-44C1-8968-171DD3C88C91.jpeg. Those really shouldn’t be moved/​edited/​managed from outside the Photos app, as that would mess up the database.

For photos in your iCloud Photos library, those would not be in the backup, at least not in full res. There may be low res cached versions.

Time Machine itself is a managed database, with timestamp folders per backup, and loads of aliases — not intended to be manually browsed for photos per se. Don’t change anything; treat it as read-only for anything but Time Machine itself. The Preview app can easily overwrite with changes (without manual saving), so that would be a dangerous tool for this.