Does Jetson Xavier NX support 2 HDMI monitors?

Not correct.

There are nodes

sor0_hdmi_display,
sor0_dp_display
sor1_hdmi_display
sor1_dp_display.

Thus, if you want to use HDMI, you need to disable dp node and enable the hdmi node. If you are not familiar with device tree structure, find someone who is familiar with linux kernel to help you out.