On Linux, you can hold a modifier key to drag a window. Opera has to support drag for selection, I think a modifier key like Alt is the best you'll get.
Same issue for me, there appear to be a few sources with this issue. Thus far I've identified:
NYT
Bloomberg
Some WSJ secondary feeds
VICE News
It's a worryingly large percentage of the "Recommended" sources. I really love Personal News, but without some of these key sources I may eventually have to switch (especially as a paying subscriber of both NYT and WSJ).
From Terminal.app, type
mv ~/Library/Application\ Support/com.operasoftware.Opera ~/Library/Application\ Support/com.operasoftware.OperaBackup
Then try starting Opera again. It'll start from a clean profile (so no bookmarks, preferences, etc) but we'll have your profile backed up. If this works maybe we can figure out what's causing the problem with your profile after that 🙂