UNISON have published some information on this and you can read more here https://www.unison.org.uk/news/article/2021/06/unison-joins-the-fight-over-proper-use-of-health-data/
However please note that the date has now been put back from 1 July to 1 September 2021 as detailed here. https://digital.nhs.uk/data-and-information/data-collections-and-data-sets/data-collections/general-practice-data-for-planning-and-research . This link also gives a bit more information too.
In simple terms if this is of concern to you then you can opt out of the data sharing.