I am not sure about fit files, but you can create your own workout, use some predefined or sync with trainingpeaks and distribute to device. In attachment example of my custom test training. On computer you choose training and it guides you throughout with details which zone you are or should be. I also attach how training screen looks like (it is the same on computer, you can freely customize 4 bottom panels). There is also an option to mimic real ride - you cycle indoors on routes you have ridden irl, although I haven’t tested it yet - for me it’s pointless as I don’t have smart trainer yet. After the training computer rates how well you performed on each stage of predefined workout, you can set goals to speed, cadence, power zones, hr zones, hr, power, %FTP.
I only would like to have more predefined workouts (for now only 8 are available) but you can create your own quite neatly so it’s acceptable.