I have this issue as well. macOS High Sierra 10.13.2 Macbook Air.

I don't understand the point of fullscreen mode without the ability to type in the address bar because it is not there.

Show toolbar in fullscreen mode is greyed out for me as well. Here is what it looks like when I click on View:

Just went to the regular Cache folder and there are 1288 files in there.

Description:
I have 383 files in my Cache on my Mac under the Opera folder.
Steps to reproduce:

1. On a Mac Go to folder ~/Library/Caches
2. Under com.operasoftware.Opera then go to Media Cache
3. This is where the insane amount of cache files are

I was trying to figure out why my system storage levels were so high on my MBA. Over 50% of my drive was being used by the System Files. I searched online and step one was removing Cache Files and when I went to Opera I found all these files.

I know on iOS the Password Manager is under "Share".

For instance I use LastPass.

On mobile I hit the Opera button at the bottom of the page. Then Share and tap LastPass.

I have a rare image that I cannot find on the internet anywhere as my Opera for Mac Theme. I would like to know if it is possible to access this file somewhere on the computer or a way to save the theme.

My other question that has me thinking is: Is it possible to synchronize themes in between computers with an Opera profile/synchronization enabled?