Hestia thinks you’re using a RedHat-based OS because the /etc/sysconfig directory exists.
The correct solution is to rename the /etc/sysconfig directory, as it doesn’t exist by default on Debian or Ubuntu systems. Alternatively, you could modify the Hestia script but keep in mind that your changes will be overwritten during the next update.
sed -i -E 's|/etc/sysconfig|/etc/ZsysconfigZ|' /usr/local/hestia/bin/v-list-sys-services
v-list-sys-services | grep clamav