Driving a car in Naoshima

We are an elderly couple and planning to visit Naoshima in September. We don't know how to ride a bike and walking or waiting for the bus under the sun is a bit tough for us. We are thinking of renting a car and drive around the island. Anything we need to pay attention to? Any experience to share?

Driving a car on Naoshima won’t be of much help. The Island is small and the Benesse House Museum sites for example are inaccessible by car. Benesse, Chichu Museum etc. you should take bus from Miyanoura port or Honmura port to Tsutsujiso bus stop then walk/ use free shuttle bus to get between the different museums. For Honmura Art Houses you should take the bus to the Honmura bus stop and then walk between the art houses … the area is very small so hopefully not too arduous for you. Hopefully you aren’t there in August/ September??? There is one taxi on the island, but again it will be of limited use to you getting between sites.

Here is the page on Benesse’s website that explains transportation around Naoshima. I think there is a link to the bus schedule as well … if not I can find it for you.
https://benesse-artsite.jp/en/access/naoshima/

I understand there are two taxis on Naoshima when I checked recently, but not necessarily very useful.
Renting a car, there is a rental agency on the island - see https://ougiya-naoshima.jp/english/rental.html
One of the larger issues would be parking, and as noted above, some of the locations you would want to get to do not allow private cars.
You state "elderly" - check the age restrictions.

I'd suggest - if your budget allows it - travelling to the island on foot, spending the car rental (and extra ferry cost) fees on subsidising a night in Benesse House, then using their shuttle bus service to get around the island (and also having access to the Benesse museum before regular opening times).

Yeah! I know staying in Bernese House Residence is the best solution. Unfortunately it’s already fully booked.
Thanks anyway!
Now I planned to stay on the island for 2 nights to gain more flexibility of time. Maybe walking is good for our health (I mean slowly 😅).

Shame.
We’ve stayed there three times and every time it has delivered as an exceptional experience.
Hope you have a lovely trip