Bottom line is the objective to serve the largest group of users.
More experienced users might stumble over these things more then them.

So in the advanced/power users settings section then for instance, i would vote for that.

Having said that - i do update manually and having portable makes backuping the whole lot a wink of an eye ofcourse.
So its not a specific problem for me, but i was just querious.

There are more sides to this discussion obviously then i anticipated.
Interesting nevertheless.

Then would be the question if opera's default startup behaviour can be altered,(with parameters). never checked that.

Maybe you can add those parameters in the registry but a it may be very risky.

Then again.. im again baffeled that such an high end browser as Opera does not have a update toggle, be it in the advanced section or so. That can't be that hard to implement i should guess.

The truth is that no software maker wants people to keep using old versions of their products as it may lead to waste of their time and resources.

People using old versions of programs means more chances of complaints about problems already solved or even non-existent in newer versions, reports of issues that are related to the use of an old version and so on. And their support and QAs will have to waste time and resources dealing with them.

Im using portable(not set as default browser) - so i don't know if for instance if you start from a email-link (having opera set as default browser) if upgrade is executed, im guessing it is, proving your point.

Then would be the question if opera's default startup behaviour can be altered,(with parameters). never checked that.

With the perspective that altering the exe filename, with effective the exe "cannot be found", is not the finest way preventing the update.

Then again.. im again baffeled that such an high end browser as Opera does not have a update toggle, be it in the advanced section or so. That can't be that hard to implement i should guess.

Not hijacking this topic,just discussing in between:

The OP's qeustion was "can someone tell me how do I prevent Opera from auto update"

For me the correct way should be:
add " --disable-update"(No quote's, note the space)
to the target path of your shortcut

The problem with that one is that if Opera isn't started using the short-cut then it will be updated.

add " --disable-update"(No quote's, note the space)
to the target path of your shortcut

How does one rename the auto updater executable?

You go to Opera's installation folder and find the folder with the number of the latest build. Inside it you will find the file 'opera_autoupdate.exe'.

Right click on it and click on rename. Change the name.

Win + X -> Computer Management -> Task Manager

Regarding your question, just rename the auto updater executable.