Wrong libffi dependency version for Debian 11 (bullseye)

When trying to install on Debian 11, ghcup tells me:

Please install the following distro packages: build-essential curl libffi-dev libffi6 libgmp-dev libgmp10 libncurses-dev libncurses5 libtinfo5

However, the libffi6 package is not available in Debian; only libffi7 is available. Is v6 strictly necessary, or can it be later? And is it even necessary if libffi-dev already depends on libffi7?