About ChromeOS / ChromiumOS
Chromium OS (or Chrome OS) is an operating system designed by Google that is based on the GNU/Linux kernel and uses Google Chrome web browser as its main user interface. CloudReady is the free, easy way to convert your computer to Chrome.
Steps
Go to Client Area > Config Generator in our web site, choose ChromeOS and other options.
Download files: you need user certificate "user.p12" file and Openvpn connection "<filename>.onc" file. (If you download the ".zip" archive format that contains "user.p12" and "<filename>.onc" you must extract the archive to have the two files outside the archive as two single files on the system. See How to Unzip Files on ChromeOS.)
Click your bottom-right panel, and then the gear to open the control panel.
Type "certificates" in the search box and select Manage Certificates. In some version of ChromeOS the certificates menu entry is accessible only in the browser: open chrome://settings/certificates in the browser
On "Your Certificates" tab, click "IMPORT AND BIND", and select the "user.p12" file. If asked, leave password empty. You should now see your certificate and “(hardware-backed)” if done correctly.
Note: if "IMPORT AND BIND" is not available it's because in your device TPM chip is disabled or not available, see here. With no Bind ("hardware-backed") certificates the VPN connection cannot work.
In the browser, open chrome://net-internals , and click ChromeOS at the bottom
Choose File. Select the .onc file. It will look like it did nothing.
Now in your bottom-right panel, you will have a VPN connection.
Click to connect. If you are forced to enter a password, type anything, it doesn't matter what.
Check whether connection is ok in the bottom-right panel.
Many thanks to @nopcode85 for his help.