Try deleting the "Sessions" folder in "/Users/yourusername/Library/Application Support/com.operasoftware.Opera/Default". You'll lose all open tabs, but that will probably fix it.

If needed, you can start Opera in safe mode in a terminal like this:

"/Applications/Opera.app/Contents/MacOS/Opera" --disable-gpu --no-experiments --disable-extensions --disable-update

Then, you can goto the URL opera://flags and reset your flags and turn Early Bird off in settings. Then, close Opera and start Opera normally.