Install extlinux by entering the following commands in the terminal:
sudo apt update sudo apt install extlinux
Description:
collection of bootloaders (Linux ext2/ext3/ext4, btrfs, and xfs bootloader)
syslinux is a suite of bootloaders, currently supporting DOS FAT and NTFS filesystems (SYSLINUX), Linux ext2/ext3/ext4, btrfs, and xfs filesystems (EXTLINUX), PXE network boots (PXELINUX), or ISO 9660 CD-ROMs (ISOLINUX). . This package contains the bootloader for Linux ext2/ext3/ext4, btrfs, and xfs filesystems (EXTLINUX).
Homepage: http://www.syslinux.org/
Version: 3:6.03+dfsg1-2
Section: universe/utils