Hidden profile and filtering

I know how to filter a thread to just show one user’s posts, but it doesn’t work if the user has their profile hidden. Is there an alternative way to do this?

I’m a bit baffled why hiding the profile removes this functionality in the first place.

Go to the search function - the eyeglass looking thing in the top right. Type in @ then the person’s username. Then check the box for search this topic. That person’s posts show up.