https://rosolinoblog.wordpress.com/2020/01/29/adesso-gioco-con-questo/

https://youtu.be/2ngq1xJJs40

https://youtu.be/p8g6cfSeYos

https://appelsiini.net/2018/calibrate-magnetometer/

In ogni caso potrai calibrare la bussola con lo sketc figure8_calibration.ino ruotando in varie direzioni M5STACK

In any case, you can calibrate the compass with the sketc figure8_calibration.ino by rotating in various directions M5STACK

Prova questa libreria
https://github.com/Seeed-Studio/Grove_3_Axis_Compass_V2.0_BMM150

poi modifica BMM150_I2C_Address 0x13 con 0x10 nel file bmm150_defs.h

in questo modo dovresti poter accedere al BMM150.
Purtroppo M5STACK ha i magneti sul fondo

Try this library
https://github.com/Seeed-Studio/Grove_3_Axis_Compass_V2.0_BMM150

then modify BMM150_I2C_Address 0x13 with 0x10 in the file bmm150_defs.h

this way you should be able to access the BMM150.
Unfortunately M5STACK has magnets on the bottom