Comment # 6 on bug 1210964 from Thorsten Kukuk

I have the same Notebook and that works fine with openSUSE Tumbleweed, which
uses the same bootloader configuration.
You need UEFI, if you enable or disable secure boot does not matter. But you
have to decide before the installation what you want to use: installing with
disabled secure boot and enable it later is in general not a good idea,
independent of MicroOS or Tumbleweed.

(In reply to Doe from comment #5)

> Could it be that MicroOS is "made just for UEFI-clients"?

No, MicroOS works with all kinds of firmware like Tumbleweed.

> I wonder if the Lenovo default value "Legacy/UEFI: both", "Legacy first"
> leads to my problem.

Could be, I don't remember what the default was.

> Should I install MicroOS with secure boot and UEFI-only mode again? MicroOS
> seems to use GPT, so in my opinion this kicks out Legacy-Clients with only
> BIOS, or am I wrong?

GPT has nothing to do with legacy or UEFI firmware.
I would suggest to switch to UEFI only, so that no part of the system get's
confused and makes a wrong assumption and install new.