From display settings options I've setting PORTRAIT screen orientation. If I perform a SHUTDOWN and then switch on the setting remains as set in portrait , if I run a Windows 10 RESTART the setting, after Windows reboot, returns to landscape.
I'm using a NUC8i3BRK with 8GB RAM and M.2 da 240GB disk, OS Windows 10 IOT Enterprise
After changing the display orientation to Portrait, did you confirmed this mode by clicking on "Keep my changes".
I've checked in two NUCs (however not in NUC8i3BEK and the display remains in portrait also after restart.
Instead to setting this mode from Windows settings, you may try to do this from Intel Command Control Center (IDCC). Check in start menu under letter " I". If the IDCC is not installed on your system, you may download it from Microsoft Store.