I don’t think the OpenVPN support on Chrome OS is being maintained anymore. I no longer do any testing with it. The OpenVPN client from the Google Play store should be used instead.
Then I think you should take it out of this page Pritunl - Platform and Device Support as It misleading.As for openvpn client can it support google single sign on?
Also some of our chrome os is chrome os flex which doesn’t have play store so that can not be used.