Keys are accessible but I would like text appears as it does correctly on my NUC4 e.g.
Good. There is a debate among some of us about this. As I said, some say it is by design, some say bios error. Back years ago, this would have been called "a bug-like feature".
You have to decide about secure boot, now that you know what the issue is. Personally, I would keep secure boot on, and hope for a future bios update.
Intel says it is design future. I say it is bad design. However, you should know that even when the Secure Boot is enabled and the functional keys menu is invisible, still the keys are accepted.
We'll see in future BIOS updates. The point is when text is displayed, we know when it's the right time for pushing the F-key (it's not too early either too late).