That didn't work

Opera: 137.0.6036.63 (updated automatically from 136.0.6008.80)
OS: Windows 11 Pro, per-user install (%LOCALAPPDATA%\Programs\Opera)

The problem

I don't want the Opera browser assistant (browser_assistant.exe) running. "Run at startup" is off (installer_prefs.json has "run-at-startup": false, and there's no Run-key entry). To make sure it stayed off, I also put a deny-execute permission on the assistant folder. That held for about a month: assistant.log shows no activity from 16 Sep to 19 Oct.

On 19 Oct a silent automatic update to 137.0.6036.63 undid all of it in about 20 seconds:

1. It reinstalled the assistant as an "extra app"
2. It reset the folder's permissions, which removed my deny entry
3. It recreated the Opera scheduled assistant Autoupdate <id> scheduled task (logon + daily triggers)
4. It started browser_assistant.exe immediately

The autoupdater passed --run-at-startup=1 even though my saved preference is false. It also passed --pintotaskbar=1.

Permissions can't keep it blocked: the installer runs as my user account, and I own the folder, so it can always rewrite the permissions.

Questions for Opera

• Is there a supported way to opt out of the assistant that survives updates? For example a setting, an installer flag such as --with-assistant=0, or a policy?
• Why does the autoupdater pass --run-at-startup=1 when the saved preference is false?
• Could updates leave the assistant alone if the user has removed or disabled it?

Workaround (until there's a real fix)

A small script, run as SYSTEM every 10 minutes from Task Scheduler. It kills the assistant, deletes the assistant's update task, and puts back a deny-execute entry on browser_assistant.exe only. It leaves the rest of the folder alone, so browser updates can still run the assistant installer and won't fail.

Save as C:\Program Files\OperaAssistantWatchdog\watchdog.cmd. Editing Program Files needs admin rights, which is what you want for a script that runs as SYSTEM. Change the first two set lines to match your machine:

@echo off
setlocal
set "EXE=C:\Users\YOURNAME\AppData\Local\Programs\Opera\assistant\browser_assistant.exe"
set "ACCOUNT=YOURPC\YOURNAME"
set "LOG=%~dp0watchdog.log"

tasklist /fi "imagename eq browser_assistant.exe" /nh | find /i "browser_assistant.exe" >nul
if errorlevel 1 goto tasks
taskkill /f /im browser_assistant.exe >nul 2>&1
call :log Killed browser_assistant.exe

:tasks
for /f "tokens=1 delims=," %%T in ('schtasks /query /fo csv /nh 2^>nul ^| findstr /i /c:"Opera scheduled assistant Autoupdate"') do (
    schtasks /delete /tn %%T /f >nul 2>&1 && call :log Deleted task %%~T
)

if not exist "%EXE%" goto done
icacls "%EXE%" | find "(DENY)" >nul
if not errorlevel 1 goto done
icacls "%EXE%" /deny "%ACCOUNT%":(X) >nul && call :log Re-applied execute deny

:done
exit /b 0

:log
>>"%LOG%" echo %date% %time% %*
exit /b 0

Schedule it from an elevated command prompt:

schtasks /create /tn "Opera Assistant Watchdog" /ru SYSTEM /sc minute /mo 10 ^ /tr "cmd.exe /c \"C:\Program Files\OperaAssistantWatchdog\watchdog.cmd\""

It only writes to watchdog.log when it actually does something, so after the next Opera update you should see one "Killed / Deleted task / Re-applied" set of lines in the log file.

Downside: after an update, the assistant can run for up to 10 minutes before the script catches it. A proper opt-out from Opera would be much better.

How to disable the tray icon?

This C:\Users\YourUserName\AppData\Local\Programs\Opera\assistant\browser_assistant.exe keeps starting due to a Scheduled Task:

\Opera scheduled assistant Autoupdate 1773662556
  Action: C:\Users\UserName\AppData\Local\Programs\Opera\autoupdate\opera_  autoupdate.exe
      --scheduledtask --productiscomponent
      --installdir="...\Opera\assistant" --producttype=assistant
Triggers: At logon (UserName, 5 min delay)  +  Daily at 08:10:45
Enabled: True   Next run: 9/17/2026 8:10:45 AM

The 1773662556 in the task name is the app_id in assistant\installation_status.json — so this task is specifically the Opera Browser Assistant component's updater/launcher.
opera_autoupdate.exe runs, updates the component, starts browser_assistant.exe, then exits.

It is not in any registry Run key, either Startup folder, or a service. There are two sibling tasks for Opera itself (Opera scheduled Autoupdate 1710858113 for the user install, ...1675775403 for the Program Files one); those are the browser's own updater, separate from this tray-assistant.

Also note installer_prefs.json has "run-at-startup": false — that setting governs the Opera browser, not this component, so it doesn't have any bearing here.

To stop browser_assistant.exe just this one time:

Disable the task from a cmd prompt (reversible, keeps Assistant updatable if you re-enable):

Disable-ScheduledTask -TaskName 'Opera scheduled assistant Autoupdate 1773662556'

Or remove the scheduled task outright:

Unregister-ScheduledTask -TaskName 'Opera scheduled assistant Autoupdate 1773662556' -Confirm:$false

Caveat: Opera's own updater (autoupdate: true in installer_prefs.json) tends to recreate component tasks on the next browser update. If it comes back, you'll have to run those commands again.

Can this be disabled from the Opera settings?

No, there isn't any settings for it; "Browser Assistant" is a background system component (like the crash-reporter/updater), not a feature with a Settings-page switch. So "disable in Opera's settings" isn't possible.

The closest equivalent — block the executable from ever running again, without deleting anything (fully reversible) — is to deny execute permission on it via ACL:

icacls "C:\Users\%USERNAME%\AppData\Local\Programs\Opera\assistant\browser_assistant.exe" /deny %USERNAME%:(RX)

icacls "C:\Users\%USERNAME%\AppData\Local\Programs\Opera\assistant\assistant_installer.exe" /deny %USERNAME%:(RX)

To check the result:
icacls "C:\Users\%USERNAME%\AppData\Local\Programs\Opera\assistant\browser_assistant.exe"

And to undo (remove the deny rule) later:
icacls "C:\Users\%USERNAME%\AppData\Local\Programs\Opera\assistant\browser_assistant.exe" /remove:d %USERNAME%

icacls "C:\Users\%USERNAME%\AppData\Local\Programs\Opera\assistant\assistant_installer.exe" /remove:d %USERNAME%