Hi
Yes, the end of post boot phase can be monitored by HSE_STATUS_INIT_OK:


You can read the status directly. See struct hseAttrSmrCoreStatus_t in HSE Service API reference manual:

You can find an example for Get Attribute service in HSE DemoExamples:
https://www.nxp.com/webapp/Download?colCode=S32K3_HSE_DemoExamples
This is from c:\NXP\S32K3_HSE_DemoExamples_1_0_0\S32K3_HSE_DemoExamples\Secure_Boot\S32K344_Advanced_SecureBoot:
/* Get status of the Secure Memory Region and Core Reset Entry installation */
HseResponse = Get_Attr(
HSE_SMR_CORE_BOOT_STATUS_ATTR_ID,
sizeof(hseAttrSmrCoreStatus_t),
(void *)(&smrCoreStatus));
ASSERT(HSE_SRV_RSP_OK == HseResponse);
Regards,
Lukas