I understood it as c) only UUID7, no secondary external UUID. The external Id is used instead of Bigint because you don't want your external users to query 1,

I understood it as c) only UUID7, no secondary external UUID. The external Id is used instead of Bigint because you don't want your external users to query 1, then 2, then 3 (IDOR)... But the random part of the Uuid7 makes this impossible. Uuid7 isn't a substitute for Created/Updated, but a substitute for the dual field Uuid4/Bigint.