I see Zwift support Computrainer - it is not ANT+ FE-C.
But there are other old trainers - need support also.
There are many programmers that do reverse engineer for his trainer and can control his trainer from c++ program.
And they try to do virtual usb stick device with ANT+ FE-C support.
They stuck on it - with ant api can easy work with existing ANT+ FE-C device , but simulate virtual device - very hard task. Or need change hardware part - easier buy new trainer.
Need do very simple protocol with few functions: initTrainer, startTrainer, stopTrainer , controlTrainer. In controlTrainer can set resistance and get current speed, cadence, resistance from trainer.
Many programmes that have other trainers can himself write support for his trainers. Need only simply way to communicate with Zwift.