https://docs.hex-rays.com/9.0/developer-guide/idapython/idapython-porting-guide-ida-9
please refer to the documentation.
The largest change is due to the removal of two modules:
ida_struct
ida_enum
For years now, those 2 modules have been superseded by the ida_typeinf module, which offers similar functionality.
https://docs.hex-rays.com/9.0/developer-guide/idapython/idapython-porting-guide-ida-9
please refer to the documentation.