Best posts made by TKTK2001

I finally found the solution:
There is a blue vertical bar right under the Opera-window closing button (red "X").

Didn't even thought this was a button at first.

I clicked it and the quick access to the extensions reappeared. -> Just need to click on the cube and then on the extension, just like in the other browsers.

I hope this is helpful if someone has the same problem.

@mr-panther You can also try installing ad-blocker extensions. uBlock Origin seems to work great till now.