When using SAI for I2S, STM32CubeIDE does not give you the option to choose Mono mode. It's only option is Stereo Mode. However, STM32 SAI HAL supports both SAI_STEREOMODE as well as SAI_MONOMODE, so I think this should be an option.
I am using I2S with a mono .wav file. If I use I2S in stereo mode, the .wav file is played twice as fast. By manually changing hsai_BlockA1.Init.MonoStereoMode to mono mode in sai.c, the .wav file plays normally
I am using a Nucleo-L432KC with STM32CubeIDE 1.2.0. If I enable SAI1 in I2S mode, the only option is for Output Mode is Stereo, though the SAI HAL file supports Mono mode as well.
This is also an issue for me in CubeMX 5.3.0. Deleting the MBEDTLS_CONFIG_FILE without the single quotes gets the project to compile. It appears to be a bug in CubeMX. Hope they fix it in a future version.