I would suggest to have a look to UM2688 for the high speed data logging, https://www.st.com/resource/en/user_manual/dm00685314-getting-started-with-the-stm32cube-high-speed-datalog-function-pack-for-stwin-evaluation-kits-stmicroelectronics.pdf , the data format is explained there in details including the JSON file configurations, tagging etc.
