I would expect that if you have a smart folder of Projects as you described, any view of Users (board or table or whatever) would default to taking the assignee relation as the context filter.
However, context filters work for to-many relations, so you can’t choose a to-one relation.
Perhaps you can send a screenshot of the Project db and also one of what the context filter looks like at the moment
Sorry, I hadn’t picked up on the capital A for Assignees, meaning that you were using the native assignment field.
I agree, it should work, but appears not to. Let me dig into it and get back to you.
It turns out that enabling Assignees as a route for context filtering carries the risk of generating a large number of paths which could be overwhelming, so it was not supported.
However, we’re going to rethink this and you should see an update soon.