Eine optionale Desktop-Ansicht (wie in Mozilla Firefox oder Google Chrome) wäre sehr wünschenswert.

What is your version of Opera and which operating system do you use (Debian/Ubuntu/Linux Mint, type in terminal: lsb_release -a and uname -a)?
See:
https://forums.opera.com/topic/17195/how-to-post-about-a-problem-in-opera

Auto-filling and saving forms as well as login credentials would also be great (save on request and save manually in settings).

Add private/secure search engines like DuckDuckGo, Ixquick/Startpage, Metager, …, please!
User defined search engines should be able to set as default search engines.