I’m not sure if this applies to the Orbitty board but I have seen on one of our (D3) custom carrier boards that the DTB that is flashed with JetPack results in HDMI not working. As a workaround we use flash.sh to update the DTB with ours and the system functions properly afterward.
Our BSP is not yet compatible with Jetpack release 4.2.1, our software team is currently working on a new BSP which will be released soon, please check back on our support page. We are expecting an update by the end of this week for this release.