Same here:
https://techtablets.com/forum/topic/tbook-16-power-no-os-selection-screen-on-boot/
Did you run the “Boot to Windows” app or use the option in the Shutdown/Restart menu (long press Power)?
I’ve been doing the latter until now, has been working fine. This problem only surfaced after the one time I used the app. I “restored optimized defaults” in the EUFI, no effect. I think the app breaks the OS Selection screen.
Hmm… what setting has to be changed to get the OS Selection screen to come back? Gurus?