Default filter in report data for different user

I don't think you can make the default filter different for different users in the Reports section, no. Not if they're logging into Qualtrics with their own accounts and accessing the Reports section.
But you can definitely set up separate custom reports for different users, with whatever filters you want. And if you really don't want User A seeing User B's filtered data (and vice versa), then I would not give the users permission to access to the entire Reports section. Instead, I would just use public report links, giving each user access to only their report. You can do that in the Reports section by clicking "Share Report," then "Manage Public Report," then check the box to make "Public Report Available." Copy that link and share it with the appropriate user.