After a thought, I’m starting to lean towards the battery for some of your problems too, the same as the others above. I’ve had a battery before that’s failed after a few months.
The rp maybe different and I’m surprised it’s giving no codes - as I say, a warm favourite is a vacuum leak
The keyfob? I would be trying a new battery in it first if none of the buttons are working - starting the car has nothing to do with the battery in the fob