Google announced the June 2021 core update on June 2, 2021, with Danny Sullivan writing: "Later today, we are releasing a broad core update, as we do several times per year. It is called the June 2021 Core Update." Google put its usual one-to-two-week estimate on the rollout and later confirmed it was complete as of June 12, 2021, roughly 10 days after it began.
What made it unusual was the pairing. Google said some of its planned improvements were not ready in June, so it shipped the parts that were and followed with the rest as the July 2021 core update, cautioning that "it's possible a very small slice of content might see changes in June that reverse in July." Search Engine Land's launch coverage carries the full announcement.
As a broad core update there was nothing specific to fix and no penalty to lift. Google's standing advice applies: audit the pages that lost visibility against the self-assessment questions in its core updates documentation and improve overall helpfulness. Some movement between core updates is possible, but the most significant recovery typically registers at a later core update; our recovery guide covers the sequence.