You've posted in a BMW i3 forum, not a BMW X3 forum. Please post in the correct forum where you'd almost certainly get much more help.
For what it's worth, an i3 defaults to Comfort mode and will start in that mode regardless of the driving mode when last shut down. In an i3, the default driving mode can be changed by changing the value of a parameter that controls the default driving mode. To make this change, a smartphone app used with an OBD to WiFi or Bluetooth or BMW's proprietary eSys desktop software used with an interface cable must be used. I don't know whether such a change is supported in the X3 iDrive version.
[22-04-25 to now] 2019 BMW i3 Imperial Blue Metallic, Giga World, Tech + Driving Assist, Heat Pump, 428 Wheels
[14-11-05 to 22-06-15] 2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging