Most rental cars I've used already had 100% fuel, so I definitely had to return them at the same level. I think there is a little more flexibility with ICE, since analog fuel gauges are probably less accurate than EV charge level meters.

So I was usually able to find a gas station near the airport rental, and get as close as possible to topping off (if the car was a full tank when I first picked it up). I've never tried to rent an EV, so I'm not sure how easy that would be in a comparable situation. Probably not very.