Hello,
I don't think there is currently a desktop Opera setting that completely removes local bookmarks from the address bar suggestions while keeping the bookmarks themselves.
The address bar uses bookmarks as one of its suggestion sources, and the available settings mainly control things like search suggestions and browsing history. The Android version having a separate option doesn't necessarily mean the same control is available on Opera for Windows.
If you want to keep the bookmarks but prevent them from appearing in the suggestions, I don't know of a reliable flag in opera://flags that does this. Those flags can also change between Opera versions, so I wouldn't recommend relying on an old flag you find online.
One thing you could try is checking Settings > Privacy & security > Address bar, if that section is available in your version of Opera, and seeing whether there is a bookmark-specific option. If there isn't one, it looks like deleting or moving the bookmarks would be the only practical workaround at the moment.
If anyone knows of a current Opera desktop setting that specifically disables bookmark suggestions, I'd be interested to know too.
Regards,
Malcolm