A Manjaro user on a Dell XPS 13 Plus lost their GRUB bootloader after an update, a common issue in dual-boot setups. The system uses BTRFS for `/` and `/home` partitions with a UEFI-formatted EFI partition. This guide provides a step-by-step fix using a Live USB to restore boot access.

The process begins by identifying partitions with `lsblk -f`, then mounting the top-level BTRFS volume and listing subvolumes like `@`, `@cache`, and `@log`. Correctly mounting each subvolume and the separate home partition is critical before binding system directories like `/dev`, `/proc`, and `/sys` to the Live USB environment.

Finally, a chroot into the installed system allows executing `grub-install` for x86_64-efi and regenerating the configuration with `grub-mkconfig`. This method is vital for recovering from a failed update that corrupts the bootloader, ensuring the dual-boot system remains functional.