I had wondered about the bolded parts above too. I don't think my battery capacity would go below 80% in the next few months. With that assumption, I recently asked Apple via chat if they would be able to replace the battery if I paid for it. They said yes, that I don't have to wait for it to drop to <80% before requesting paid service.
The only time, as I understand from that chat, that Apple won't replace the battery if capacity is >= to 80% is if you are asking for battery replacement under warranty. Under warranty, they won't replace the battery under that condition.
I suppose it makes sense. If you want to pay for an earlier replacement you're welcome to do that under Apple. That's what I plan to do in September. In any case, my 12Pro has long since expired its warranty.