Howto rebuild the grub for mate 18.10 Says no efi directory


I tried chroot ubuntu mate running its live usb drive into newly installed ubuntu mate residing on a 32gb usb3 drive.

While following advice from an article I ran into a problem right after grub-mkdevicemap command grub-install, the error was no efi directory found, so I went and looked into /boot/ and there it was "/boot/efi" yet after inputing --efi-directory=/boot/efi the program said it doesn't look like an efi directory, I just ignored it and went to type update-grub to finish, but it still doesn't show ubuntu mate from the usb drive in the list of storage devices.

I did this rebuilding attempt cause for some reason the ubuntu mate installer replaced my windows 10 boot manager from showing for the second time and showing "ubuntu" to boot from.

Is there a proper way to chroot? am i doing it wrong? I used debian chrooting method which should be similar. The error tho is no efi directory message. I converted the mbr to gpt on this usb drive using diskpart from windows 10 and then checking successfuly it had gpt which it said it did, but something is still wrong, do I have to convert to gpt using a linux tool? I'll try finding info about this.

Anyway my goal is to rebuild the boot loader on the gpt usb drive. I wanna be able to use this usb drive on mutiple pcs like a rescue disk not depending on a grub loader installed on some other drive.