Does the SD Card Library in MPLAB® Harmony support a 4-bit SD bus mode?
For the 4-bit SD bus mode, an SD Host controller is required. There is an SDHC driver and a related file system demo available in MPLAB® Harmony that supports this.
Demo location: <install folder>\apps\fs\sdcard_fat_single_disk\
Configuration: pic32mz_da_sk_adma