We need documentation from Sierra to show that the CWE and NVU update packages are signed and verified by corresponding modules. We also need documentation showing how Secure boot is implemented (specifically saying that the Hardware Trust store is used). Specifically for the EM7590, EM7411 and EM7455.
Did you contact distributor to get these documentation?
Btw, if i remember correctly, em7455 does not have secure boot feature