Ok, I kinda found a workaround for this annoying problem.
Looks like it's tied to another bug which makes opera start in windowed mode all the time.
So when I start opera in a window the context menu works fine, but as soon as I use the maximize button to go full screen it stops working.
So, instead of using the button on the window use the keyboard shortcut ALT+F10 (or whichever shortcut you have for this, you can find out in settings) to switch between window and full screen. Then the issue isn't present.
You can use the minimize button normally, looks like only the maximize button causes this.
Hope it helps
P.S. That's on Ubuntu 22.04