Here is a link to the suggestion in the official issue tracker

opera.atlassian.net/servicedesk/customer/portal/9/BS-63731

I am having the same problem. Why is it using ESC to exit fullscreen?
And why is there no option to turn off this nonsense.

As always there is a problem and it's only in Opera 😞

https://play.geforcenow.com/ Opera Geforce Now is having problems with games due to the fixed ESC. We cannot enter the menus of the games.

Does it appear if you enable if via the menu (View -> Show Toolbar in Full Screen Mode)?

I am joining the group of unsatisfied Opera users on Mac running Mojave. Version 56.0.3051.116 and this bug is still not fixed. Can somebody do something about it? It drives me crazy and obviously other users too. Thanks? ...