The Litchi documentation does include a user’s guide which makes clear what functions are supported. A quick search of that documentation does not reveal any mention of IMU calibration. It would be impractical for Litchi to list functions that it does not support. Such a list would have to be updated whenever a feature was added to a DJI drone that Litchi does not (yet) support. Another user has compiled a list of functions for which the DJI app is still required. It may not be 100% complete but should be pretty close:
An IMU calibration should only be necessary in limited circumstances such as a hard crash or the drone malfunctioning in some way. It also requires a level surface. Why is it that you need to re-calibrate the IMU before every flight?
For curiosity sake, what is this other app that can calibrate the IMU?