More people now work from home at least some days, and they look at homes differently because of it.
Space and quiet
A spare room is ideal, but a quiet corner with a door or partition can do. Check noise from the road and from neighbours.
Connectivity
Ask which broadband providers serve the building and what speeds residents get. Check mobile signal inside the flat as well.
Amenities nearby
Coworking spaces, cafes and a gym close by make remote work easier on days you want to step out.