It amazes me that people seem to think that once they have clocked in for work they have entered some kind of dystopian dictatorship where all their rights are immediately forfeited. And that people are fundamentally not allowed to push back against this kind of bullshit.
What right is forfeited? The only reasonable assumption to make is that your boss can read everything. Regardless of if you think it is fair or not it is still the safest assumption.