PEP 384 and PEP 652 define a stable ABI to be used with Python 3.2 and later.  On Windows, symbols for the stable ABI are exported from the python3.dll shared library.

The following functions are present in Python 3.9 but have been removed from Python 3.10b3:

PyObject_AsCharBuffer()
PyObject_AsReadBuffer()
PyObject_AsWriteBuffer()
PyObject_CheckReadBuffer()

The justification for the removal of these functions was discussed in this issue:

https://bugs.python.org/issue41103

Without these functions, an extension cannot utilize the stable ABI to access the buffer memory of data structures.  The buffer protocol is suggested as an alternative, but the buffer functions PyObject_GetBuffer() and PyBuffer_Release() are not present in the stable ABI.

While these two functions may be added to the stable ABI, removal of the four functions above makes Python 3.10 incompatible with previous versions.  It is requested that the four functions be reinstated and maintained as described in PEP 652.

That removal was reverted. Thanks for the report!

They are still deprecated, which means they may be removed from future API (and only remain in the stable ABI).
But I hope that's only considered when the new buffer protocol is available in the stable ABI.