Google announced on July 1, 2021 that "The July 2021 Core Update, previously announced, is now rolling out", adding that "These typically take 1-2 weeks to finish." On July 12 Google declared the rollout "effectively complete", 12 days after it began.
The update was the second half of a pair. When announcing the June 2021 core update, Google explained that "some of our planned improvements for the June 2021 update aren't quite ready, so we're moving ahead with the parts that are, then we will follow with the rest with the July 2021 update", and warned that a very small slice of content might see June changes reverse in July. Search Engine Land reported data providers saw the July rollout as notably smaller than June, with ranking movement concentrated around July 2, July 9 and the final day.
With the pair complete, Google's standing core-update guidance applies: there is nothing specific to fix, so audit the pages that lost visibility against the self-assessment questions in the core updates documentation, invest in overall helpfulness, and expect meaningful recovery to register at a future core update. Our recovery guide covers the sequence.