Yes with this command
sudo grub-install /dev/sda
make sure efi partition is mounted
then
grub-install –efi-directory that_efi_path
So the command is
sudo grub install –efi-directory /dev/sda2
??
sudo grub-install –efi-directory /mnt /dev/sda
Yes done
Let me try it
sudo grub-install /dev/sda
you could always dualboot via usb


not so sure, try reboot

https://askubuntu.com/questions/685122/what-should-i-do-to-get-ubuntu-dual-boot-with-windows-10-on-this-toshiba-laptop
I’ve tried several approaches and it still boots directly to Windows 10. It is a Toshiba Satellite Radius L15W-B1208X with Windows 10 the original OS.
I read and tried to follow all prerequisite s…

not so sure, try reboot
Windows is still starting first

you could always dualboot via usb
How??
The only way to access Linux is from the recovery mode page of windows

How??
The only way to access Linux is from the recovery mode page of windows
click the link

click the link
Okay

i fear i cant help much more, .. such.doesnt happen on my debian
Do you a way to modify EFI boot Loader and set something like
default =/dev/sda8??

Do you a way to modify EFI boot Loader and set something like
default =/dev/sda8??
on the page i saw something ‘efibootmgr’ ..

Okay
It says to download the latest bios update for Toshiba
Download EasyUEFI and use it to adjust the boot order. This tool is pretty easy to use; just move the “Ubuntu” entry to the top of the list. If there are multiple entries, move one that refers to shimx64.efi, not one that refers to grubx64.efi.
Open an Administrator Command Prompt window (not the newer shell in Windows 10; the older classic Command Prompt) and type bcdedit /set {bootmgr} path EFIubuntushimx64.efi.
If these procedures both fail, you could try using an EFI shell and its bcfg command, as described here. Note, however, that you’ll need to disable Secure Boot to get the EFI shell to launch, and you’ll need to copy the shell program to a USB flash drive as EFI/BOOT/bootx64.efi, then boot that drive.
If all of this fails, I recommend you return the computer for a refund,
EasyUEFI is a free software which allows you to manage the EFI/UEFI boot options & the EFI System Partitions. With this software you can easily fix EFI/UEFI boot issues, such as missing or corrupt EFI/UEFI boot option, missing or corrupt EFI System Partition.

There are two things you might attempt:
Download EasyUEFI and use it to adjust the boot order. This tool is pretty easy to use; just move the “Ubuntu” entry to the top of the list. If there are multiple entries, move one that refers to shimx64.efi, not one that refers to grubx64.efi.
Open an Administrator Command Prompt window (not the newer shell in Windows 10; the older classic Command Prompt) and type bcdedit /set {bootmgr} path EFIubuntushimx64.efi.
If these procedures both fail, you could try using an EFI shell and its bcfg command, as described here. Note, however, that you’ll need to disable Secure Boot to get the EFI shell to launch, and you’ll need to copy the shell program to a USB flash drive as EFI/BOOT/bootx64.efi, then boot that drive.
If all of this fails, I recommend you return the computer for a refund,
Let me download EasyUEFI