I am in China. I installed Opera (the latest stable version) on Ubuntu 18 with:
sudo snap install opera
Opera looks good. The default search engine is Google. That is not so good in China, you cannot access Google without VPN.
I set the default search engine to Bing.
The Chinese search engine Baidu is useful, when you, for instance, want to look up Tang dynasty poetry with explanations.
I think I may have set baidu.com as the default, just to try it. Later I just added it as a link in the Speed Dial tab.
I had Opera open all day yesterday. This morning, when I reopened Opera, I saw the Chinese takeover!
Opera now has Sugou (another Chinese search engine) as default. This cannot be changed from within Opera, nor from without, it seems.
Also, it is not possible to add Bing to the search engines. I can click the button Add in search engines settings. A little window opens which wants me to enter a url. But the Add button here is disabled.
It is not possible to add another search engine.
Opera comes with a few commercial links on the Speed Dial tab, but the Chinese have added many more.
snap remove --purge opera
There is a folder snap in my home directory. It contains a folder opera.
There is a text file Preferences. I can see the nefarious Sugou link in there. There is a Preferences.backup
I deleted, Preferences, changed Preferences.backup to Preferences.
Then I reinstalled. But the Chinese problem persists.
browser.js reinstalled itself, Preferences was written to Preferences.backup and Sugou is back in Preferences.
I do not know where the what script is doing this.
Can you help me get my Opera back under control??