Previously I installed Ubuntu 16.04 and used an external hard disk, which its partition format was NTFS, as its /home. Recently I tried to upgrade to Ubuntu 20.04 by installing a new one and removing old one. Although I wanted to keep data that are stored in /home. So during the installation I selected Something else option and did delete/format /root, boot and ... . But wrongly I select use as ext4 from drop down list when I wanted to set mount point of external hard disk as /home. After completing the installation the I saw the problem: grub rescue error. At first I tried to fix that by reinstalling grub; bit the problem was not that. Because when I was unplugging the external hard disk the OS could boot (although in a long time) and when it was plugged, I saw grub rescue error.
Now I installed Ubuntu 20.04 for using temporarily and backing up data from external hard disk by connecting it to a machine with MS Windows OS and using ext2explorer. But want to reinstall Ubuntu and use external hard disk as its /home again. I think it may be possible to be done by selecting Something else and deleting/formatting hard disk and setting it as /home. But it takes a long time for restring backed up data from MS Windows to the external hard disk after installing Ubuntu. Is it possible to install Ubuntu and set external hard as /home without doing those?