If your kid is only ever riding on the flat (school commuting is normally like that) then he does not even need any gears at all, and you’d be better off not buying something that will rust up if left outside and need repair and adjustment (which I’m guessing you’d not be familiar with). Simple bikes are best for Taipei, unless you can bring it inside under cover every day. If you do live on top of a long hill, then gears are a good idea. Not for riding along Neihu road, though.
He definitely does not need suspension, front or back, for the city streets. On cheaper bikes, suspension is more of a liability than a blessing, and it’s heavier and more expensive and less robust than solid forks. Only needed for rocky unpaved tracks, not even for dirt roads in general, and definitely not for asphalt.
Of course, will the bike be cool enough? Who knows. A granny bike probably would not be terribly cool, but I see kids riding them all the time, and they still seem to have friends. More cool bikes for city commuting for high school kids would include the BMX style, but they’d be a second step rather than a first bike.