As I read there, this is a similar package as the os-prober
in Arch Linux. Theoretically it would help if there is a problem in this. But if UEFI somehow blocks entry, then it'll not help I think.
Beyond that, the problem has been solved!
- I changed MBR table on eMMC back to GPT.
- I used Rufus to burn 64bit ISO to flash drive with GPT table for UEFI settings. (I had 32bit before (too late I searched for the architecture of my new small netbook))
- I set BIOS settings to pure UEFI... with Secure Boot ENABLED.
- During the installation, an EFI boot partition was created along with a common boot partition.
I have tried many installations and I don't know exactly where the error was. Maybe in Secure Boot enabling and maybe in architecture. Thank you Antikythera for your willingness to help