I am trying to dual-boot Ubuntu 18.04 from an external SSD from my Lenovo Flex 5. I have already got it working on my desktop but it seems Lenovo restricts booting into anything but Windows, and I want to be able to work with the same OS on both devices.
So far I have backed up my EFI partition and replaced \efi\boot\bootx64.efi with grubx64.efi to override the restriction. From here I am not sure where to go because I already have Ubuntu installed on the SSD and I just want to be able to boot from it, and I have not been able to find any documentation on this.
Thank you for your help.