I've tried clearing the BIOS and resetting it as recommended. No success
I've tried to disable drives. Still no success. But as I wrote in the first post: my Toshiba is not NVMe - it is SATA M.2.
So finally I found some time to read carefully Dortania's OpenCore Install Guide and make my own EFI folder. It is not tested yet, but when creating I found:
Configuration Notes
In some cases where you cannot set the DVMT-prealloc of these cards to 64MB or higher in your UEFI Setup, you may get a kernel panic. Usually they're configured for 32MB of DVMT-prealloc, in that case add these values to the iGPU properties:
Key Type Value
============================================
framebuffer-patch-enable Data 01000000
framebuffer-stolenmem Data 00003001
framebuffer-fbmem Data 00009000
============================================
https://dortania.github.io/OpenCore-Install-Guide/config-laptop.plist/kaby-lake.html#deviceproperties
So in short, DVMT is important and there are two possibilities:
change DVMT value, which you can read about in many guides, e.g. here:
or change the OC configuration as described in Dortania's Guide.
This change is not only required to have 4K output on HDMI. It is required also for install/run macOS system.
Quickly I corrected config.plist files in the EFI folders, both from @Akerbeltz14 and from @takobaba, and the installation program started. Now I hope it will go further without additional problems
marcinkk's post in Dell 7280 - problem with install with shared OC EFI folders was marked as the answer