When I worked on the configuration of GD23_T4, I followed the comments expressed here in the forum. I still don't have a Teensy 4 to test its operation.
Upload some photos of your arrangement, so I will have an idea of how teensy 4 works with full power.
It was only a theoretical approach, based on the comments I followed in the forum regarding the operation of the Teensy 4 SPI bus.
The next step is to get a pair of these fantastic chips to adjust the playback of assets, images and audio. and video files, using the SdFat beta library that Greiman recently shared with us.