The solution given works for me. The only thing I've noticed is that the highlight on the main menu accessible from the Opera button is missing when using the dark theme; with the light theme everything seems normal for me. Every site I've visited works, including YouTube. Considering that Ubuntu 16.04 Xenial, a long term support version of the OS, is supported until April 2021 it's a real pity that Opera 69 and above can only now be installed by rebuilding a deb package. Surely Opera should always run on all LTS versions of Ubuntu while they continue to be supported? Otherwise people who have been loyally using Opera for years, in this case over four years, will suddenly find that their system no longer updates via the Opera repository and that the lastest deb packages can't be installed on their system without any warning.