Orin nx disk encryption, the device cannot boot normally

Sorry I’m not sure if it is a known issue in JP5.1.2 but you could also verify with Jetpack 5.1.3, which is the latest release of JP5.x currently.

If you can work with Jetpack 6.0GA (R36.3), then you can just stay on that.
Or do you have any requirement to use Jetpack 5.x?

You can also refer to the following thread about the steps to enable disk-encryption for Orin NX with Jetpack 5.1.2, which has been verified from us.
Disk Encryption on Orin NX NVMe Not working - #22 by JerryChang