You can add to context menus via Settings > File Types.
Removing items depends on the type of item.
In some cases, it's easier to block the shell extensions that add them using a tool like ShellExView, if they don't have proper options to turn off their menu items within the respective programs.
You can also hide all of them by default and explicitly add back just the ones you want. See but see Tip: Organise and Speed-Up Context Menus for how to do that.
Other methods that add/remove menu items from File Explorer should generally work in Opus, but some are specific to File Explorer.
Regarding BitDefender, AFAIK the only option is to use a better antivirus that doesn't block its menus from everything but Explorer. Something both they and Norton do for reasons no one from either company has ever taken the time to explain, despite many users asking them. See Bitdefender context menu not showing - #2 by Leo -- ESET NOD32 is a good alternative.