See also the bpo-39947: "[C API] Make the PyThreadState structure opaque (move it to the internal C API)". Recently, I also added helper functions:
* PyThreadState_GetFrame(): Python 3.9 and limited C API version 3.10
* PyThreadState_GetID(): Python 3.9 and limited C API version 3.10
* PyThreadState_GetInterpreter(): Python 3.9 and limited C API version 3.10
* PyThreadState_EnterTracing(), PyThreadState_LeaveTracing(): Python 3.11
See also pending GH-29121 of bpo-39947: "Add PyThreadState_SetTrace() function".