or you can just open the task manager then go to the startup tab and uncheck Opera Browser Assistant.

@pilis00 I was talking about the startup.. mine also install fast.. another question .. 3 actually:

1. why does opera auto-start with windows like some malware ?
2. why is there no option to disable this in settings ?
3. why are there no answers to the first two questions on google ?

after some actual detective work:
the option is in the "On Startup" section called..
"Run when my computer starts"

it really should not be enabled by default..

I dont really use Opera, I sometime use it to test a new web page im working on..
but I found this a deterring factor since the competition (chrome, edge, firefox) installs in seconds...
so whats up with that ?
is chrome intentionally delaying it ?
weird..

@itsmeray @donq both of your methods will not prevent it from starting again once its somehow reinstalled ... my method works 100%

or you can just open the task manager then go to the startup tab and uncheck Opera Browser Assistant.