This is driving me nuts!
As of 63.0.3368.71, when you start Opera the standard Ctrl+Shift+Home & Ctrl+Shift+End Windows shortcuts (to select everything until the start or end of text) stop working everywhere in Windows while Opera is running. Just to be sure, I confirmed that once Opera has exited those 2 shortcuts work again. It took me a while to figure it out, so it may have started earlier than 63.0.3368.71 but it definitely happens with that version. It's like Opera takes over those 2 shortcuts but doesn't do anything with it. I tried looking for them in the Opera settings and didn't find anything either.
Tried to disable all my extensions, same result.