One method we use is sticky notes. If people are afraid to have their name attached to an idea (or complaint) then the anonymity of sticky notes helps.
It also helps get the introverts to submit ideas when there are extroverts dominating the discussion. Another way to encourage input is to use apps the keep the submitter’s identity private. “Incogneato” is one app I’m aware of.
See if the method of solicitation helps bring that person into the conversation.