Hi,
We are able to follow the steps and set up environment on host PC. Please try to clone the image again and check if you are able to generate the files.
$ sudo ./flash.sh -r -k APP -G r3261.img jetson-tx2 mmcblk0p1
user@user:~/nvidia/nvidia_sdk/JetPack_4.6_Linux_JETSON_TX2_TARGETS/Lin
ux_for_Tegra$ ll r3261.img*
-rwxr-xr-x 1 root root 14788465108 十一 18 13:47 r3261.img*
-rw-r--r-- 1 root root 30064771072 十一 18 14:05 r3261.img.raw
And then follow the steps to mount r3261.img.raw.