the solution without nesting:

• https://stackoverflow.com/questions/55728957/apache-failed-at-step-namespace
  
• https://help.directadmin.com/item.php?id=614

$ sudo sed -i -e 's,PrivateTmp=true,PrivateTmp=false\nNoNewPrivileges=yes,g' /lib/systemd/system/apache2.service
$ sudo systemctl daemon-reload
$ sudo systemctl start apache2.service
$ sudo systemctl status apache2.service

Oder wie man es richtig mit systemd macht but direct editing of service configuration file is not so beautiful. It's better to edit it by `systemctl edit apache2` command or create override config:

$ sudo cat  << EOF >> /etc/systemd/system/apache2.service.d/override.conf
# /lib/systemd/system/apache2.service
[Service]
PrivateTmp=false
NoNewPrivileges=yes
EOF
 
sudo systemctl daemon-reload
sudo systemctl start apache2.service