I have reinstalled Raspberry Pi deskop (Debian Stretch Linux for the Intel platform) from its DVD Image on an Intel based platform recognised as x86_64 (output of "uname -r") and i386 (output of "dpkg --print-architecture") architecture.
Have updated the OS with the usual "sudo apt-get update ; sudo apt-get -y upgrade" commands and, right after, manually installed the libc6:amd64 package with the command "sudo apt install libc6:amd64".
After all that, I fired the PiHole installation process with the known commands, and everything just worked fine - the installation process ran smooth - no errors; the UNIX processes are all running fine upon installation completion including the intially failed pihole-FTL process.
I now have access to the admin page after its installation. 