The only real info we have is steam player numbers, MS haven't released any PR at all which probably says everything. If it had been a big success we would have been told how many players have played, "biggest forza launch ever" etc etc.
I posted this info in another thread which puts how bad the Steam numbers are into context.
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.
I've got 12 hours played so far. I feel it's a decent racing game but not a $70 title, so I'm glad I didn't pay for it. I don't think there's enough there to justify the price-tag and there are bugs.