Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32n6/STM32N645/SDMMC1/SDMMC_FIFOTHRR#0x0
THR=B_0x0
SDMMC data FIFO threshold register
FIFO threshold
0 (B_0x0): threshold = 0 byte (no threshold)
https://github.com/modm-io/cmsis-svd-stm32