My cat hides all day and only comes out when the house is quiet. Is he unhappy?

The fact that he comes out at night and seems relaxed tells you something important: he is not anxious all the time. He has found conditions in which he feels safe, and he is using them. That is actually a sign of a cat who is coping, not a cat who is suffering constantly. But you are right to notice that something has shifted, and working from home is a very plausible cause.

For cats who are sensitive to activity and noise, a person being home all day is genuinely more stimulating and unpredictable than an empty house. When you were out, the flat had a rhythm he understood. Now there are movements, voices, video calls, the energy of another presence all day long. Some cats adapt easily. Others find it genuinely harder to regulate, and they do what he is doing: they withdraw until conditions feel manageable again.

This does not mean he is miserable. It means he needs more predictable safe zones and probably more environmental structure than he currently has. Covered beds in his preferred hiding spots, high shelves he can access, and times in the day when the space is quieter or less active can all help. If the hiding has increased progressively over the past few months rather than being stable, that is worth looking at more closely. The Work With Me assessment asks about exactly this kind of gradual change, and it is often where the useful detail lives.