Before I was gifted a Apple Watch, I bought a cheap Amazfit band (= Xiaomi's band, you can never tell which one is the rebranded one), as they have an API you can get access to, but it doesn't really work that well in practice. I never got approved for the dev API and the reverse engineered API[0] doesn't return all the data either.
In the end I resorted to storing all the data in the Health App and using an app[1] to export the data as a CSV file and push it to my server. The benefit of using this approach is that then the actual device does not matter and you can use whatever fitness tracker you want.
If you are on android, you can use apps like Gadgetbridge[2] and FitoTrack[3] to achieve something similar with some of the Chinese bands. But, I am not sure about how to auto export
In the end I resorted to storing all the data in the Health App and using an app[1] to export the data as a CSV file and push it to my server. The benefit of using this approach is that then the actual device does not matter and you can use whatever fitness tracker you want.
If you are on android, you can use apps like Gadgetbridge[2] and FitoTrack[3] to achieve something similar with some of the Chinese bands. But, I am not sure about how to auto export
[0] https://korniichuk.medium.com/export-xiaomi-data-87f7e284b37... [1] https://www.healthexportapp.com [2] https://gadgetbridge.org [3] https://codeberg.org/jannis/FitoTrack