It's not a place to show how good Software Engineer is by removing Title Bar and created something similar but hard to use. It's user experience & usage. (UI, UX). I could accept that someone still prefer to use LYNX, but not me.

Computer is made to help people.

The system (Gnome, Wayland, Mac, Window$) has its own Windows Manager system that people get used to it.
Now I have problem to use Opera because the Title Bar was gone. Opera becomes a rebellion in among the applications. Hard to use.

If Opera's developers wanted to show off programming skills, please have something that provides all compatible/synchronized functionalities as the Title Bar has (different system might have its own behaviour).

The original opera developers had moved to Vivaldi, it provides a check box in settings to use System's Frame/Theme that could bring back the Title Bar & Border.

Looks like the Opera Developers are Windoz heads to favor Windoz users' requests with no reason (https://autohotkey.com/board/topic/66060-opera-11-remove-titlebar-but-keep-taskbar/)
And it even removed the option to bring back System's setting like Vivaldi does. (So you have to stay with Windoz).
The intension (Windoz like UI, no response to Linux Users' requests) is so obvious. And it's your choice to stay with it.

Good luck!

@alamyliu Looks like there were something happened, and the Opera update days ago still keeps the unfriendly design. I'm switching to Vivaldi (by old Opera developer).

It's not a place to show how good Software Engineer is by removing Title Bar and created something similar but hard to use. It's user experience & usage. (UI, UX). I could accept that someone still prefer to use LYNX, but not me.

Computer is made to help people.

The system (Gnome, Wayland, Mac, Window$) has its own Windows Manager system that people get used to it.
Now I have problem to use Opera because the Title Bar was gone. Opera becomes a rebellion in among the applications. Hard to use.

If Opera's developers wanted to show off programming skills, please have something that provides all compatible/synchronized functionalities as the Title Bar has (different system might have its own behaviour).