http://spywarcbzke2e6skl7wjwtmmnrkslue24cld6kfcufjhhwxtceogmuad.onion/articles/opera.html
From their FAQ (the message used to be there in 2017, they must have deleted it somewhere in 2018 ): Opera has not officialy open sourced its browser . However, leaks of the old Presto web engine Opera used to use have appeared on the internet. Even with that however, there could still other spyware might be hiding in there.