If you are using ProtonVPN for your cell phone, you can also use it on an Ubuntu Linux installation. Here is the official guide, and I can confirm that it works and the guide is excellent.
Essentially installation on Ubuntu 20.04 involves going into your Ubuntu settings and selecting “network”, and hitting the “+” at VPN. From there you will “Import from file” and select the VPN config file you downloaded from the official guide. Once this file is selected, you can enter in your ‘OpenVPN / IKEv2 username’ from the ProtoVPN Dashboard “Account” section. Your new VPN configuration is ready and can be selected in the upper right-hand network icon.