I found this entry explaining this:
https://www.reddit.com/r/operabrowser/wiki/opera/known_issues/#wiki_.22add_to_speed_dial.22_keyboard_shortcut_command_is_missing

The problem is that a I have some thousands of bookmarks and adding a bookmark with Ctrl+D delays a whole minute.
Ctrl+B works just fine in my situation.

There's a way to asign this functionality again, I don't want to stop to use Opera GX just for this situation, It is one of my main reasons to use it.