UTC is not heavily split in the current catalog, but the short label still hides the underlying IANA zone and any future policy change. The safe pattern is to write the abbreviation for humans and the zone for machines.
Etc/UTC sits on UTC year-round in current rules, which makes UTC unusually stable for cross-system timestamps. Even so, civil-time policy can change, so an explicit zone reference is still the safest store.
UTC works well as a global baseline, but it does not tell you whether a local place follows daylight saving time. That is why city pages still need IANA zones — UTC is the storage primitive, not the local-clock answer.
Within this single zone (Etc/UTC, +00:00), UTC is unambiguous, so the abbreviation and the IANA zone effectively interchange.