Until Ubuntu fixes the “Rust Coreutils” issues on Ubuntu 26.04 you can use this quick fix. It simply creates the relevant Gnu Coreutils aliases.

Just copy the below and put it in your ~/.bashrc file.

################################################################################
# Force GNU coreutils instead of Ubuntu 26.04's default uutils
if command -v coreutils >/dev/null; then
    for cmd in $(coreutils --list); do
        if command -v "gnu$cmd" >/dev/null; then
            alias "$cmd=gnu$cmd"
        fi
    done
    unset cmd
fi
################################################################################