Near 70 years old, I was surprised how much my new Zwift riding helped this winter and spring. Any Zwift group ride needs 95% pedaling time; no coasting or you are dropped. And the pedal resistance on my Kickr v5 is subtly different than riding outdoors -- there's no "micro coasting" within a pedal stroke. That helped with a more efficient pedal stroke, more like "pedaling in circles". I notice the difference on the road this year.
The custom Zone 2 workout that I made was really good for me. a short warmup, then 8 minutes Zone 2 wattage, 30 seconds free ride--to get off the saddle! Repeat for 45 to 75 minutes. And I can bump or reduce the target wattage: 95%, 110%, etc. The trainer adapts to whatever cadence I'm using, adjusting the resistance to keep the watts consistent.
My cycling goal is just for general riding fitness, 40-50 miles and 2200-3000 feet of climbing. I'm not looking for PRs. So Zone 2 for endurance, and selected hill climb attacks for speed and power.