You may want to copy the iPhoto Library from the external drive to your Pictures folder.
Then try to migrate the library to Photos .
- If your Mac is running macOS 12 Monterey or an earlier system version, you can launch Photos while holding down the options key and select the saved iPhoto Library from the dialog to select a library to open it in Photos. This will create a new Photos library with the photos and albums from your iPhoto Library.
- On macOS Ventura we can no longer convert iPhoto Libraries, but you can try to import the photos: Launch Photos, then use the command "File > Import" and select the iPhoto Library you copied to your Pictures folder. Then click the button "Check for Import" and import the photos to your Photos Library. This will only import the photos, not the albums and the keywords, however.