Is their a way to downgrade from Jetson Linux 36.3 to Jetson Linux 35.4.1 which runs jetpack 5.1.2 (Ubuntu 20.04.5 )?
You could only reflash the whole board with sdkmanager.
Tried 20+ times, when I reaches 97% it fails, however just install ubuntu 20.0.4 with JP 6.0.
Even fully erased my NVMe, it has to be something else.
Based on the data from Nvidia it requires Linux 35 not 36.
There is nothing called “Linux 35”…It is rel-35 or rel-36.
When you flash Jetpack5, they are all rel-35 based BSP and when you flash jetpack6, they are all rel-36 BSP. rel-35 and rel-36 are the software installed to your Jetson. Not something for the host PC.
Share your sdkmanager full flash log to us so that I can check why your flash got failure.