This document defines an extension to the timestamp format defined in RFC 3339 for representing additional information, including a time zone. It updates RFC 3339 in the specific interpretation of the local offset Z, which is no longer understood to "imply that UTC is the preferred reference point for the specified time".

While not strictly ISO 8601, it’s closely related. RFC 3339 was/is basically a subset of ISO 8601, allowing only what’s strictly “needed” or really universal: e.g. 2024-05-27, 2024-03-13 12:34:56Z, etc., nothing like 2018-W06-1 or 2018-036.
Now what’s really interesting is how additional data for timestamps was added. For example, specifying the human-readable timezone name, instead of just the UTC offset: 2022-07-08T00:14:07Z[Europe/Paris].