I have tried flash Jetpack 6 onto a Jetson AGX Orin 64GB Developer Kit. My host system has 20.04. I have tried using both SDK Manager 2.1.0.111682 x86_64 and flashing through Quick Start — Jetson Linux Developer Guide documentation.
Both of them have been unsucceful. I used Jpetack 5.1 and it was working fine.