You may also refer to Workflow 6: Initrd Massflash from Linux_for_Tegra/tools/kernel_flash/README_initrd_flash.txt for your use case.
Try the following command after you finish l4t_initrd_flash.sh to switch your board booting from NVMe.
$ sudo ./flash.sh jetson-xavier-nx-devkit nvme0n1p1
Or the following instruction to modify and re-build UEFI.
Initrd flash boot order - #26 by WayneWWW
Both of above methods do not need serial console.