That’s normal. The lower cadence hurts your legs more and the higher cadence takes pressure of your legs and more on your heart rate.
When I was younger and very quick (and before injury) I used to average cadence over 100 (outdoor rides - before Zwift existed). It was just natural.
Lower cadence can be used to benefit if you want to do long steady intervals at 90% FTP. I use those when I’m training for riding in mountains overseas, I don’t have those mountains near where I live. When I’m then riding at normal cadence then it’s not so hard, even with the altitude difference. I just look at what I’m training for, if it’s a 40min climb, then 4x10min is that - I just make the rest periods in between the intervals shorter as I get used to them or increase the power slightly (or both if things are going well).
These days I usually have around 80-85 cadence.
It’s also good to get used to riding with high cadence as well, especially if you get into riding on the track. In sprints I would be up at 160-170rpm.
In any case, learn as much as you can, if you can ride with some local pro cyclists, try and learn from them as much as you can, try different things and adapt different training methods and find what works for you.