This is incomplete. For a proxy it’s more like
foreman-installer \
# Stop the puppet agent
--puppet-runmode none \
# Unmanage the puppet server
--puppet-server false \
# Inform the foreman proxy this node has no puppet master
--foreman-proxy-puppet false \
# Inform the foreman proxy this node has no puppet ca
--foreman-proxy-puppetca false \
# Do not attempt to install certificates
--foreman-proxy-content-puppet false
For the katello server itself you want to add --katello-enable-puppet false as well.
This is from the top of my head. I may have missed some things.