Recently (since today) I've noticed some of the questions are highlighted as in the picture below. What does it mean and how does it work?
These are questions either tagged with your favourite tags or tagged with tags you are most active in.
Checking your profile I don't see any favourite tags, so it must be the latter.
Stack Exchange is trying to make a best guess as to what you might be interested in. To get more appropriate questions set up some favourite tags.