I did it!
https://armbian.com/ja/boards/luckfox-rk3308b-nova
I've also included a script called “novaconfig” for manipulating GPIO, so feel free to use it.
The PDM mics works perfectly like this, but it seems the pin on my Nova is broken, so I can only record up to 6 channels.
I'm going to buy another one for maintenance, so thanks, Luckfox! Here's to the future.