The installation of the package rhasspy_amd64.deb (2.5.11) fails with Bullseye because the dependent package libgfortran4 cannot be installed.
The libgfortran5 package is used in Bullseye.
p.s. I have corrected the dependency in the package:
dpkg-deb --extract rhasspy_amd64.deb tmp
dpkg-deb --control rhasspy_amd64.deb tmp/DEBIAN
sed -n -i ‘s/libgfortran4/libgfortran5/gp’ ./tmp/DEBIAN/control
dpkg --build tmp rhasspy_amd64.deb
dpkg -i ./rhasspy_amd64.deb