The official guide from Proton, https://protonvpn.com/support/ios-vpn-setup/, requires the use of “OpenVPN Connect” app.

Some inspiration from this guide: https://surfshark.com/blog/how-to-setup-vpn-on-iphone, tells me that I can possibly setup vpn manually on iOS via:

Go to Settings > General > VPN & Device Management > Click on the VPN tab.

Click on Add VPN Configuration.

. .

However, I will need the following information::

• Type: IKEv2.

• Description: Your preferred name of the connection.

• Server: The hostname of the server.

• Remote ID: Copy the hostname you put in the Server line.

• Local ID: Leave it empty.

• User Authentication: Username.

• Username: Put in the service credentials,.

• Password: Put in the service credentials,.

• Proxy: Off.