What is the maximum number of PDM digital microphones that can be handled with the SAI interface? What will be the best way to interface with around 20 PDM microphones?

[ALuo.4]

Hello, if I understand correctly from the document (https://www.st.com/resource/en/application_note/an5027-interfacing-pdm-digital-microphones-using-stm32-mcus-and-mpus-stmicroelectronics.pdf), the SAI interface can only handle at most 8 PDM digital microphones. In this case, what will be the best way to deal with more than 8 PDM microphones? Thank you in advance!