1. Download and unzip the file vpn-UDP4-1194-config-2.5.2.ovpn from the Nextcloud VPN Files folder.
2. In the Ubuntu settings, go to Networks.
3. In the VPN section, press the + button, choose the Import from file… option and select the file downloaded in the previous step.
4. In the Identity tab, enter your username and password.
5. In the IPv4 tab, in the DNS section, uncheck Automatic , enter the DNS 193.144.75.9, 193.144.75.12 as shown in the screenshot and in the Routes section check Use this connection only for resources on its network.
6. Finally, click on the Add button.

To connect, tap the indicators in the upper right corner and select VPN » Connect (if you have multiple VPN connections set up, you'll need to select the appropriate one).

To disconnect, tap the indicators again and select VPN » Disconnect.