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

Source : https://stackoverflow.com/questions/65040703/apache2-failed-to-set-up-mount-namespacing-permission-denied