~50 tiny equally spaced lights moving in a single-file line formation

Spotted with two others from my balcony in the Edgewater neighborhood of Chicago. We live under an O’Hare flight path so planes are a common sight, but this was completely different. At about 10:15 pm CDT on May 22, 2021, we observed a single-file line of equally-spaced tiny, white, unblinking lights traveling NE. They looked like tiny individual pixels in the sky – no discernable shape other than individual dots/squares. There were probably 50 of them or so and the entire sighting lasted about 10 minutes. Another onlooker described them as moving stars. Seems plausible that it was a line of aircraft flying exceptionally high and in formation. We checked flightradar24 as it was happening but didn’t see anything besides low-flying aircraft flying west on their O’Hare approach (which were also visible).