@rafi rosenberg if you wanted to somehow "assign" a card to a person, without them being able to edit it, then they can't be a member of the board and you should use a label to identify a card as belonging to that person. You can filter a board based on label just the same as you can by card member, however those cards won't show up in the person's Cards view.
They can see the board if it's team visible and they are a member of the team, and you can disable "self join", you can also control comments. You can also, as @marc suggests, add an Observer to a board if you have a Business Class team.
If you had to thrive a new habit during a lockdown, what would it be? Trello
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