If there is one universal truth of human biology, it is that exercise is good. It is good if you do a bit or a lot, if you are young, old, male, female, trans, pregnant, trying to get pregnant, single, married, divorced, depressed, a smoker, have cancer, have heart disease, have dementia, an astronaut, a pure mathematician, a plumber, tall, short, liberal, conservative etc etc. There isn't anyone that doesn't benefit…
I worry about my health and often I have a really good try and making a habit. But crap is it hard. It's not the money or the time. There's something else about willpower and boredom. I wish I could get on an exercise bike, stare at a brainwashing device, and "wake up" an hour later having remembered none of it.
But most cardio should be easy, like 60-70% your training maximum heart rate. Many elite distance runners follow an “80/20” rule, where 80% of their training is easy in this way. But 100% is fine also. If you’re not used to it, this feels odd, like you’re going too slow and doing nothing. But measure your time and distance and the improvements will be obvious. It’s like training for free. The only ingredient is time. After a good long low-intensity run I feel less fatigued than I did when I started. Meanwhile hordes of people suffer through these awful spinning classes. It’s like they think exercise should make you feel worse instead of better!
People who feel the need to put in effort and who aren’t distance athletes are likely much better served by adding HIIT and/or strength training than by pushing steady-state cardio too hard.