What you are describing is the expected behaviour after the upgrade to macOS 13 Ventura. Dave you perhaps upgraded to macOS 13 Ventura or Sonoma and the system version below your post is no longer valid (iMac, OS X 10.11)?
The Ventura added another nail to the coffin of iPhoto and Aperture. The Photos.app can no longer convert iPhoto or Aperture libraries to Photos Library. The only way to access our photos in iPhoto Libraries is to use the command File > Import in Photos and then select the iPhoto Library.
- The iPhoto Library should be located in a supported location, for example your Pictures folder. If it is on external drive, the drive should be compatible - not a NAS, not a Time Machine volume, the file system format should be APFS or MacOS Extended.
- After you select the iPhoto Library for importing from, wait. Photos will show you a ist of new photos, that are not yet in your Photos Library and you can import them.
You could use this method to convert your iPhoto Libraries to Photos Libraries, by importing the photos from the old libraries into a new, empty Photos Library. This will only import photos and videos, not the albums, events, photos, and the keywords will be lost. See: Import photos from another library in Photos on Mac – Apple Support (UK)
If you own a licence for the full version of PowerPhotos, you could use PowerPhotos to convert your remaining iPhoto Libraries to Photos Libraries. The most recent version of PowerPhotos supports this, similar to the old iPhoto Library Manager. This way you could save your albums.