Wow, you’re right - while there is an option to ignore words per level, there is none for DWs!?
Not sure whether or not it used to be there, over the past 2 years or so I’ve rarely used the web site anymore.
FWIW, I just tried this out. Starting a preview session and flagging a word as difficult won’t work either - the flag just doesn’t survive the session (yet another bug) unless you actually go through the second turn at least and thus start the “watering process” of at least one word.
Another of those inconsistencies and bugs that happen to exist across the three platforms iOS, Android and web …