Apple Health says I did 30km, but I understand why Strava wouldn't consider the first 4km an exercise – a lot of slow riding due to traffic lights etc.
Finished with about 27km and thought that I need to get the last 3km in to get a nice number. Circled around the neighbourhood a few times and succeeded!
Sometimes I really wish I had a proper road bike in addition to my single speed. If the graphs don't lie, I sometimes reached about 25–30km/h with a single speed, which is quite the achievement for me, personally. However, I would love to speed around on an actual road bike, which has higher gears so my feet wouldn't get as tired.