The Met's had an investigation open over this since 2020, all that seems to have happened as a result of this popular four-part series is that they've confirmed

The Met's had an investigation open over this since 2020, all that seems to have happened as a result of this popular four-part series is that they've confirmed they're looking into specific possible criminal offences by the Post Office or its employees that we didn't know they were looking in to before. It's not clear that this is something which started investigating because of the popular TV series, but most likely not and they were just pressured into revealing more about the existing investigation - the police here don't generally give running updates on criminal investigations to the media.