Ace Combat 8: Wings of Theve has the highest Steam peak in the series, according to SteamDB.
The tracker shows an all-time peak of 48,743 players, hit 14 hours ago. 42,612 were still in-game on the same chart.
Ace Combat 7: Skies Unknown peaked at 13,758 at its February 2019 launch, on that same tracker.
The full release is out on Steam, PS5, and Xbox Series X/S. The count is a Steam peak, not total sales.