Dont need to lookup dependencies for the "cat" command.
Its the library "ld-linux-x86-64.so.2", the 64 bits version, what the pi-hole-FTL binary wants.
Could you post results for below ones ?
uname -r -m
dpkg --print-architecture
dpkg --print-foreign-architectures
dpkg -L libc6 | grep ld-linux
sudo find / -name *ld-linux*
apt-cache search ld-linux-x86-64.so.2
EDIT: Mind I altered the find command.