I’ve used xrandr command, but it seems that the xrandr command don’t replicate the two different resolution screens.
Yes, xrandr mirror mode only supports to screens with same resolutions. Otherwise, it would out of scope in the small one.
This would be a lot of work, but often people will access a Jetson from a remote system via a virtual desktop. There are a lot of “ifs” as to whether this would be suitable for you, but there is no reason why a second monitor on a Jetson could not view an X server on its own system as if it were a remote system. This would handle scaling, but performance and resources might be an issue.
NOTE: You’d run two X servers on the Jetson, one would run as usual, the other would run only the virtual desktop client to monitor the other desktop.