The question is: Where is the list of opera command line args? switches? options?

Depending on whether Opera was installed for all users or the current user, you can do:

"%ProgramFiles%\Opera\opera.exe" --help > "%USERPROFILE%\Desktop\operahelp.txt"

or:

"%LOCALAPPDATA%\Programs\Opera\opera.exe" --help > "%USERPROFILE%\Desktop\operahelp.txt"

, press enter in the command-line window that pops up, and then look in the operahelp.txt file for some Opera-specific commands. You must do it with "opera.exe" and not "launcher.exe". You can try this for Opera GX and Opera Crypto too.

For the longest time, to start Opera in a private window, you had to use --private, instead of Chromium's --incognito. But, now Opera supports both. --private is just an alias to --incognito.

Then, if you look in the Windows Task Scheduler's library, and select the Action tab for an Opera task, you'll see:

C:\Program Files\Opera\opera.exe --scheduledautoupdate $(Arg0)

for example, where $(Arg0) will get replaced with argument 0 of the command so that:

"C:\Program Files\Opera\opera.exe" --scheduledautoupdate "C:\Program Files\Opera\opera.exe"

is executed to check for and update that Opera.

You'll also see one for the assistant like this:

C:\Program Files\Opera\opera.exe --scheduledautoupdate --component-name=assistant --component-path="C:\Program Files\Opera\assistant" $(Arg0)

For Opera GX specifically and its GX Profiles feature, you have:

"C:\Program Files\Opera GX\launcher.exe"  --side-profile-name=31323333325F343034303835323938 --side-profile-no-gx-sounds --side-profile-muted --side-profile-clear-on-exit --side-profile-minimal --with-feature:side-profiles --no-default-br

to load a specific GX profile by its name/ID, and a few forced-option switches that are optional. But, Opera GX (and regular Opera and Crypto) still support the Chromium --user-data-dir=path way if you like doing things that way to get a separate profile.

So, that's basically the Opera-specific stuff. The rest is at https://peter.sh/experiments/chromium-command-line-switches/, but there's no copy of that list that marks which ones Opera doesn't support. I don't think anyone feels like doing that. But, Opera supports a lot / most of them.

For Opera's installer, see https://www.reddit.com/r/operabrowser/wiki/opera/installer_commands/.

It seems in this days, you need to analyse each piece of software on your own to get to know how to operate it.
I'd like to sit those guys into plane, and in den middle of the flight let them know to fly on ther onw with no instruction manual. Shall they find out themselfs.

@ajaxstardust I don't think there are command lines specific for Opera, so (most of) those for Chromium should work.

What is the problem in proving this list on the opera homepage?
What is the problem of providing a changelog, so that one does not need to search for hours just to find out what the actual version is?

@ajaxstardust Chromium should work.

Is this to suggest that Opera users should switch to Chromium, since it should work; Chromium is the only properly documented browser of its type?

The point (by now) is less about understanding the software commands. I lose confidence in the whole (the software, the community, etc.) when I'm advised to reference Chromium.

The software in question is Opera. I'd prefer to be a proper Opera user. Where is the Opera documentation? A simple page to indicate that there is none would be better than spending time doing the research only to find a few bits here and there about how to open a new tab. I'm sure I didn't submit enough queries and likely omitted the most sensible keywords in those that I did. I didn't do the necessary research.

I trust your advice regarding the commands. I'll have a look. Thank you. I apologize for my outburst, and my poor attitude. I shouldn't participate in forums. I'm old, and I don't like the way things have turned out. It's no one's fault that I feel this way. It's the degenerative nature and aging. I'm sure there's a couple of Pink Floyd songs about it, or other expressions likewise.

Best regards.