The BBC One platform offers built-in English subtitles (CC) for both Series 1 and 2.
Because of the thick Aberdonian accents and specific police jargon, many viewers find English subtitles helpful for following the plot. You can find them through these official channels: Granite Harbour (2022) English subtitles
You can stream the series with subtitles through a BritBox subscription on Prime Video. The BBC One platform offers built-in English subtitles