Hey @DSoutham,
Firstly, welcome to the community!
This is not something which we have available right now and so your request is similar to this one:
We’ve reported the feedback we’ve received about extending the “hide” permission we have currently on column level to hiding items/groups on a board, either limiting to those assigned or to a specified list of users on the board.
We don’t have plans to add this immediately but it is being considered for future enhancements to the permissions so watch this space!
In the meantime, would it work to have a board per project and use a column to indicate which client the project is for/folders to achieve this?