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 , 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].