Hi jaivishnu.m,
What’s the Jetpack version in use?
It seems the SD slot is from your carrier board.
Have you confirmed that you’ve enabled the related nodes in device tree even if you can recognize it in lsblk?
It is the command expected to be used for Xavier NX eMMC module.
It is not the expected command since you are still using “Xavier NX eMMC module” rather than “Xavier NX SD module”.
To flash to SD card, you can refer to the instruction in Flashing to an SD Card.
Please also refer to About Flashing Jetson OS to Jetson Xavier NX emmc module - #7 by WayneWWW and it seems you can only mount SD card rather than boot from it.