An old avatar of mine
If you are doing high end intervals ERG mode isn’t always what you need. There is a way to disable ERG mode in Zwift without having Zwift change the turbo resistance if the terrain changes e.g. the incline changes or you ride over a bit of “feature landscape” like a wooden bridge section. It does mean manually creating a .zwo file or editing a Training Peaks file.
Here are some hints and tips on editing Zwift workout files