My 2014 prius won’t start without a jump, even with a new 12v battery. Why?

So I have a 2014 Toyota Prius with over 200,000 miles on it. It’s been a great car and I really would like to get it fixed. About a week ago it started showing symptoms that the 12 V battery was going bad. We limped it on for a week or so. When I say that I meant to say we would try and start it and it wouldn’t start on the first button press. We would have to hit the start button a few times before it would actually start. I thought,”easy! Bad 12v battery” and replaced it. That didn’t solve the issue. In any other car I’d say the alternator was bad but as we know Prius’ don’t have alternators. It will start fine off of a jump pack/box or from a car jump start and will drive until the motor shuts off. Once the motor kicks off to switch to the ev battery, it dies. Any solutions to this?