My weekly winter training usually involves 1 hard workout (examples linked below), 1 Zwift category race and the rest easy/long rides or active recovery. I retest my FTP every other week (20 min version), which is a workout in itself.
Not a fan of the "busy" fitness plans on Zwift but some of the individual workouts are excellent, in particular:
Mat Hayman's Paris Roubaix routine (who used a version of this leading up to his 2016 win):
https://whatsonzwift.com/workouts/60...-paris-roubaix
Cancellara's cruise control
https://whatsonzwift.com/workouts/le...cruise-control