Just some notes: As long as SDK Manager knows what user account name and address to use it won’t care about how this is actually accomplished. The default is via the USB cable which is emulating wired ethernet. Not only does this emulate an ethernet adapter, it also emulats a router and is able to assign address 192.168.55.100 to the host PC and 192.168.55.1 to the Xavier. So long as the host PC does not have some sort of security setup interfering this is the simplest way to go since it has no special requirements.
If you use wired ethernet, then this must be connected to a router to assign it a route, and the host PC has to be on that same router and able to reach the Xavier.
In both cases you must have completed the first boot account setup since ssh is useless without an account to connect to.
You might check ifconfig on the host and see if it has an interface with 192.168.55.100 showing (you’d need to leave the USB cable connected). Be certain you’ve completed the first boot account creation. If you use the external ethernet, then run “ifconfig” on the Jetson to see what the address is that was assigned by the router for eth0, and try to ping that from the host PC (and try to ping 192.168.55.1).