Looking at the peak player of every game published on Steam by Xbox Game Studios in the past 5 years:
Halo Infinite - 272,586 (F2P)
Halo MCC - 161,024
Forza Horizon 5 - 81,096
Age of Empire IV - 73,928
Sea of Thieves - 66,906 (Late Steam Launch)
Flight Simulator - 61,829
Forza Horizon 4 - 40,399 (Late Steam Launch)
Age of Empires II Definitive - 38,725
Ori and the Will of the Wisps - 34,807
Grounded - 32,012
State of Decay 2 - 22,728
Age of Empires III Definitive - 20,146
Gears 5 - 10,196
Gears Tactics - 7,351
Psychonauts 2 - 7,262
Hi-Fi Rush - 6,132
Minecraft Legends - 5,322
Forza Motorsport - 4,703
Minecraft Dungeons - 2,939 (Late Steam Launch)
Tell Me Why - 2,784
Age of Empires Definitive Edition - 2,708 (Late Steam Launch)
Sunset Overdrive - 2,326 (Late Steam Launch)
Pentiment - 1,250
Battle Toads - 768
Killer Instinct - 701 (Late Steam Launch)
As Dusk Falls - 300
Ignoring the games that were not simultaneous releases on Steam the only games that did worse than Forza Motorsport are As Dusk Falls, Battle Toads, Pentiment and Tell Me Why. These are truly shocking numbers. Obviously Forza Horizon is a much more popular series I think we all knew that before launch but I never expected numbers these low. I've been playing and enjoy Forza Motorsport despite it's problems but it really has bombed, at least on PC. Honestly I almost feel like this Forza should have been a F2P title with the way the career is set out.
Going to the Bethesda side of things even Redfall had a higher launch peak than Forza. Turn10 Spent longer making this than any other Forza, a 6 year development. It's to be hoped that it's done great numbers on Gamepass/Console.