I sent a ticket in on this issue, and I was right for a while the CJ4 did have reverse thrusters. I coped and paste the reply I got from Microsoft.
Support (Microsoft Flight Simulator)
Jan 28, 2021, 10:28 GMT+1
Thank you for contacting us.
The Cessna Citation CJ4 does not have reverse thrust in real life. It only goes to idle. This is now also implemented in the simulator. The previous aircraft profile was incorrect and in the latest update it was corrected.
Don’t hesitate to contact us again if you have any other issues. Have a great day!
Kind Regards,
Microsoft Flight Simulator Support Team
Pops