@Vc89 Good to know I'm not the only one.

Seems when you put Opera in full screen mode and then try to then take it out of full screen mode and then back again, the full screen mode button and the minimize buttons are greyed out. This is on the Final release of Catalina.

Tabs are not showing in Fullscreen mode on MacOS High Sierra (Stable). click on the "Show Toolbar in Fullscreen mode" is not possible because it is greyed out. I use Opera for production work since I work doing IT work remotely and need to see if the next build resolves this issue ASAP. Thanks.

So I've taken the dive and am testing out macOS Sierra DP and it seems the only applications having issues or crashing are
Opera and Opera Developer. Whenever you open Opera the memory usage goes all the way up and the machine becomes unusable.
Below is a snippet of the log from Console. Seems it has to do with the Opera Helper, I'm thinking there may be a memory leak or an incompatibility with the kernel and the browser.

Date/Time: 2016-06-13 23:24:00 -0400
OS Version: Mac OS X 10.12 (Build 16A201w)
Architecture: x86_64
Report Version: 24
Data Source: Stackshots

Command: Opera Helper
Path: /Applications/Opera Developer.app/Contents/MacOS/Opera
Version: 39.0 (39.0.2234.0)
Parent: launchd [1]
PID: 25520

Event: spin
Duration: 8.80s
Steps: 83 (100ms sampling interval, 5 samples avoided due to audio)

Hardware model: Macmini4,1
Active cpus: 2

Fan speed: 2666 rpm

I'm posting this so that the devs at Opera see this and maybe can come up with a patch or a fix in the next update
I really love the Opera browser. Thanks.