I tore my ACL last year. Ended up with about 8 weeks off the bike. I’d recommend mostly ignoring trainerroad’s AI FTP and AI workout recommendations until you feel you’re back to a reasonable level of fitness.
I started getting back on the bike 6 weeks after surgery. I was just using my Wahoo to control the trainer since I was doing like 15 minute workouts at 80-90watts. After about 4 weeks of building up to doing about 1hr/150 watts I did an AI FTP detection and tried to start using the TR recommended workouts, but they were definitely too hard. I ended up manually turning my FTP down 8% and found that to work better. Another 4 weeks later I did another AI FTP detection and at that point the AI FTP detection agreed with what I had manually turned FTP down to. That’s when things started stabilizing and the AI recommended workouts started making sense.