@leocg Deleting my ~/.config/opera folder did not get rid of the blank Settings page. I have switched to Opera developer and got rid of Opera-stable via "apt purge --autoremove opera-stable". If I'm inclined to try Opera stable again I'll download it. Fresh start.
@metarhyme You're welcome ;-)
Please keep in mind, that in some other cases in the future, you can try to disable some lists in the ad-blocker, to check which one exactly causes a trouble. That way (disabling a list, instead of switching off ad-blocker for a specific site), it may help to avoid the same or similar issue on the other sites.