@leocg I found the clue. It's a problem with Helvetica font in my windows system. The font was installed 6 times so there was a conflict on all browsers. It's not a problem with OperaGX itself. Thank you for the help !
@donlongerr Because, as you can see in the same page where you have set up DDG as your default browser, b is the trigger for searching on bing. So, everytime you use b followed by a space Opera will search on Bing.
On desktop, you can goto the URL chrome://password-manager/settings in both Opera and Chrome. In Opera, export your passwords to a CSV file. In Chrome, import the CSV file.