Opening keychain-2.db from TimeMachine backup of dead macbook.

I have a TimeMachine backup of a dead macbook. I didn't log into iCloud on this macbook.

On my new MacMini, I'm logged into iCloud, and I'm able to open the following files from the TimeMachine backup of the old macbook in the Keychain Access utility by selecting 'Add Keychain':

{Latest TimeMachine backup}/Library/Keychains/login.keychain-db

{Latest TimeMachine backup}/Library/Keychains/metadata.keychain-db

and using my old login password to unlock login.keychain-db, and the metadata password from login.keychain-db to open metadata.keychain-db.

Both of these show up in the sidebar under 'custom keychains'.

However, when I try to use 'Add Keychain' on this file

{Latest TimeMachine backup}/Library/Keychains/{UUID}/keychain-2.db

Nothing happens. I'm not prompted to enter a password, and no new items show up in the sidebar. I assume this is because I'm logged into iCloud on the MacMini, but I never was on the dead Macbook.

Is there anyway to open/import/dump the keys from the old keychain-2.db? I've been able to determine with sqlite3 that the keys I'm looking for are indeed in this file, but I'm stuck on how to open it now.

The MacMini in question is running Big Sur and I think the Macbook was running between 10.13 and 10.15.