My setup: Host PC with Ubuntu 18.04 and current SDK Manager; Xavier NX Devkit with 32GB SD card connected via USB to the host pc.
I brought the devkit into recovery mode by jumpering pins 9&10 on the button connector, power-on, and removing the jumper wire.
Started SDK Manager, selected “Xavier NX Devkit”, selected Jetpack 5.1, then start flashing.
Everything installed without errors except for the multimedia package.
(ZIP file with logs failed to upload)