Keychain Access: Can't Export in Catalina

Hello, Adayapple.

Thank you for using Apple Support Communities.

From your post, you want to export your Keychain access information to add it to your new iMac. We'd be glad to help. Are you using this article as a guide? Import and export keychain items using Keychain Access on Mac

"Export keychain items

1. In the Keychain Access app  on your Mac, select the items you want to export in the Keychain Access window.
2. Choose File > Export Items.
3. If the Export Items menu is dimmed, at least one of the selected items can’t be exported.
4. Select a location to save your keychain items, click the File Format pop-up menu, then choose a file type.
5. Click Save.
6. Enter a password.
7. The password is required to access the exported keychain items when you import them on another computer. Some exported items, such as public keys, don’t require a password.

Step #3 states a reason why Export may be greyed out.

As an alternative, you could look into iCloud Keychain: Set up iCloud Keychain

Cheers!

Hello again, Adayapple.

If you use Migration Assistant, Keychain should be copied over as stated in this article: Copy keychains to another Mac

"If you migrate your data to a different Mac using Setup Assistant, your keychains are automatically transferred to the new computer.

If you didn’t use Setup Assistant, the best way to copy your keychains to a new computer is to export and then import them using Keychain Access. See Import and export keychain items.

Note: You can’t copy passwords stored in your Local Items or iCloud Keychain. To transfer these keychain items to another computer, set up iCloud Keychain on the other computer using your iCloud user name (normally your Apple ID) and password.

You can manually copy keychains other than Local Items or iCloud Keychains to another Mac using the steps below".

1. "On your Mac, locate the keychain files you want to transfer.
2. Keychains are usually located in the Keychains folder in the Library folder in your home folder. To locate these files, press and hold the Option key and choose Go > Library, then open the Keychains folder.
3. Select the keychains you want, then press and hold the Option key and drag the selected keychains into another folder to copy them to the folder.
4. Keychain files typically end with .keychain-db. Don’t select and copy encrypted folders with names that appear as a series of numbers.
5. Transfer the folder containing the keychains to the new computer.
6. Important: Transfer the keychains in a safe manner so no unauthorized person can access them. For example, use AirDrop or a USB flash drive to copy the files.
7. Change the name of the transferred keychains on your new computer so they don’t become confused with any of the existing keychains.
8. This is especially important if you are copying a standard keychain, such as the login keychain.
9. Open Keychain Access, located in the Utilities folder in the Applications folder.
10. Add each copied keychain one by one by choosing File > Add Keychain, selecting your keychain, then clicking Add".

From this article, are these the same steps you took when copying the .db files?

Best regards.