Thanks for reaching out in Apple Support Communities. I understand that you're having trouble viewing your Photos library on your iMac and that you can only see one album. I know how important photos are; I'm happy to help. I'd suggest following the steps below to repair your Photos library:
How to use the Photos library repair tool
Let me know what you find.
If your Photos library won't open, or if Photos behaves unexpectedly, the Photos library repair tool might resolve the issues.
Follow these steps to use the Photos library repair tool:
- Hold down Option-Command while you open Photos.
- In the dialog that appears, click Repair to start the repair process.
You might be asked to type in your user account password to authorize the library repair.
The repair tool analyzes the the library's database and repairs any inconsistencies it detects. Depending on the size of your library, this might take some time. When the process is completed, Photos opens the library.
If you repair a library that's automatically updated with iCloud Photo Library, the entire contents of the library re-updates with iCloud after the repair process completes.