@Heather Smith there's no view that shows you members on a per board basis, and even if you had them in a team and remove them from the team it doesn't remove them from the board.
In order to find out definitively who has access to every board you're a member of without manually clicking through each one you'd need to use the API. The only Trello version that has this kind of control across all teams and boards is enterprise, but Business Class allows you to deactivate team members, removing them from all boards, but only within one team.
It's a good idea to create an email address for them that you can take control of (eg. via G-Suite admin) to recover full control of their Trello account if/when they leave.
If you had to thrive a new habit during a lockdown, what would it be? Trello
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