As the building of Python bindings was removed way back in January 2020 arising from issue #199 and resulting commit 84126ff, the RTAUDIO_BUILD_PYTHON option on line 48 ov CMakeLists.txt should be removed as it serves no purpose.
This option does not appear to be present in the autotools configure or meson.build, so presumably it was removed from them some time ago but CMakeLists.txt was overlooked.