You can delete Opera icons from Desktop and Start and use a Shortcut inside another folder (just known by you) or use a Launcher...

You can create another Shortcut + profile for those Guests too.

@Javilg

Depending on what are your needs, creating another profile to make the searches an then clean full browsing data each time maybe might help.

Windows 10 (x64) | Aniversary Update
Opera Stable · Beta · Developer

Test profile | Back ups Mac · Linux · Win

I, of course, have disabled search suggestions, but I still get the annoying search history.

You can't disable history suggestions.

I guess my issue is the same as the other people's. I, of course, have disabled search suggestions, but I still get the annoying search history. It's not that I have to share the computer, but that whenever I want to try (for instance) a new search changing some keywords, the bar autocompletes the previous search just because the first one or two letters are the same... it's, as I said, very annoying and it seems impossible to disable. Maybe I'm missing something, but I have tried everything in the settings.

It may seem it's not that important, but it is for me, because I'm continually searching and trying to refine the results changing keywords.

Yes, it is necessary for some people to use the machine in my Office (this one) sometimes for reasons of practicality.

You should be able to create a different user so people can use your computer without messing up with your data.

I will be sure only to use Opera on my own personal machine that only I have access to and Firefox/Chrome on machines where access by others is required.

Just remember that if someone has direct access to your computer, s/he can just get any info directly from the files.

The issue being I don't necessarily want other who have access to some of my network machines having access to my search History

To see the your history in Opera someone would need to be able to use the same Opera as you. It means that the person would need to gain access to your OS account.

I think this answers your question also?

Already done that (Prediction service) and I still get the popup making a search in the Address bar suggesting sites from search history

Ah, you want to disable history suggestions and not search suggestions.

Well, I guess it's not possible to disable suggestions from history and bookmarks.

I have also unchecked the box "Enable the search popup when selecting text under Settings>Browser>User Interface but that also doesn't stop it.

This setting has nothing to do with search suggestions.

Surely there must be a way of preventing this annoying and potentially security-challenging feature?

As already said in this topic, un-check 'Use a prediction service to help complete searches and URLs typed in the address bar' to disable search suggestions.

Surely there must be a way of preventing this annoying and potentially security-challenging feature?

Is it possible to stop these suggestions from my history

I'm not so sure about that.

and search engine from appearing when I type in the search bar?

The option you've disable should avoid search suggestions from showing up. At least this how it works here.