Hello there, when I start my laptop I get this error:
Mount: /sys/firmware/efi/efivars unknown filesystem type ‘efivars’l
Also my grub is gone, can not select OS to start. I have dualboot Manjaro KDE with Windows 10
What should I do?
Is your laptop UEFI or legacy BIOS?
If it has UEFI, you need to boot in that mode also…
It’s legacy BIOS
Then that’s why you get that error, because that filesystem is only available on UEFI systems…
But this error appeared recently. It was okay and there was grub when i first intalled the manjaro alongside windows10…
Then your system is UEFI but you boot in BIOS mode.
Also keep in mind that sometimes Windows reverts the legacy BIOS bootloader to point to his own…
To be sure reboot into your BIOS and check if you have options somewhere mentioning SecureBoot, if that is there you can be almost certain that it is UEFI 
Okay, but in BIOS there is no option to change to UEFI… I am very confused. Where should I check this settings? Do you have a pic to show me?
There never is an option to switch to UEFI because your BIOS is either UEFI or legacy.
The SecureBoot option can be anywhere depending on your BIOS/Hardware it’s different for different machines.
But maybe you can select the UEFI boot entry using your BIOS boot menu, which will be shown when you press F8 (and keep pressed) on most systems right after you turn on your computer.
Well I can’t see any of these options in my BIOS 
Then i’m unable to help more i guess.
PS: Welcome to the forum and please see:
That will help others to help you better because they will have better info about your hardware etc…
Thank you for trying Woah okay, I didn’t read that I will check it!