Does the macoOS login keychain get backed up by Time Machine backups

Yes

> in a way that could restore the keychain if the original machine's Secure Enclave is lost or destroyed?

Apparently not

"Apparently"? Is this something that can be tested with VMs?

	▲	lapcat an hour ago \| parent [-]
		I've tested with VMs. However, I'm unclear about the relationship if any between VMs and the secure enclave.