Be cautious with the MV plans. They have a lot of intensity in them. I’m in a similar situation as you - in my 40s, FTP gains hard to come by.
After some trial and error, I concluded the TR low volume plans had too much threshold workouts (in combination with my outside rides which were also reasonably hard because I live in the mountains). I replaced the threshold workouts with sweet spot. I find I can do more hours per week because I’m not as fatigued, and have better endurance.
I’d recommend listening to the podcast referenced in this post. The concept of a HR cap during sweet spot workouts has worked well for me.