Local Items Keychain

Hi Community: I'm trying - unsuccessfully - to get my iOS-re-installed Big Sur iMac to learn all the passwords contained on my Macbook Air. It's a slow learner.

I'm wary of "deleting local items keychain" even after making a back-up but how do I establish an interface by which the iMac will know the passwords on the Book?

Supplementary, in my System keychain on the iMac, there are items "<unknown>" and "Auto Unlock", which I'm unfamiliar with and which I assess as a possible attack. Any views on this?