TX2 Flash failed due to lack of bootloader

I received the following error when running the nvautoflash.sh script on my (very old) TX:

Error: None of the bootloaders are running on device. Check the UART log.

I have no idea what or where the “UART log” might be. Any help appreciated. This is the 1000 model.

Please try to install Sdkmanager on host Linux PC and flash TX2 through it. The latest Jetpack is 4.5.1:
JetPack SDK | NVIDIA Developer

Yes, that worked; after temporarily downgrading my AMD64 machine to Ubuntu 18.04 and installing SDK Manager on that OS and … then it finally worked.

Please allow the host OS for the SDK Manager to not be a dependency; 20.04 should be a viable choice for SDK Manager. In addition, other Jetson’s (ARM64) should also be viable hosts for SDK Manager.

This process is terrible.