"network-manager-openvpn-gnome" is required when configuring Purist Tunnel from the GNOME desktop. Please add it to the list of preinstalled packages (i.e. included by default on a fresh PureOS install).
From internal discussion:
David wants "network-manager-openvpn-gnome" to be preinstalled in
Fine with me. From a regular PureOS GNOME installation this would only
pull in "openvpn" and "network-manager-openvpn" etc. as dependencies,
requiring 2,542KiB of extra disk space in total.