OpenVPN for Android is installed on my Nvidia Shield. I did go through the setup instruction on:
https://protonvpn.com/support/android-vpn-setup/
But when it came to select the file, I could see the destination, where the OpenVpn.- file is saved, but I couldn't select and open the destination (USB) drive. Actually I couldn't select any destination. It was like if the app is freezing. The only option was to return to the start of OpenVPN.
Hope for an solution. Thx