I've read through this and it seems to me people get obsessed by numbers. As amateur, I presume, riders most of this is questionable.
In January 2019 I had a full scale brain haemorrhage - the "let's see if he wakes up after 10.5 hours surgery" sort of thing. I got on my bike in the May and by August was feeling pretty good. I rode my bike, no numbers, nothing, just rode it.
During the first lockdown in 2020 I rode two hours/day five days a week at the highest speeds I could maintain - 16-17mph. By mid summer I was fitter and faster than in my 20s. Today I'm 67.
Forget the numbers, trainers, turbos, etc. Get on your bike and ride it - hard.