What each UUID version is actually for: v4 for anything that must be unguessable, v7 when the value becomes a primary key and index locality matters, v1 where a MAC address in the identifier is acceptable, and v3 or v5 when the same input must always produce the same identifier.
Also: how ULID and NanoID differ from a UUID, why a v4 is not sortable, and why a time-ordered key can leak when a row was created.