I see fish falls is handicap accessible but is it accessible by wheelchair?

There is a high parking lot and from that point yes

The falls overlook would be fine but you would be unable to go on the main trail.

To the falls lookout it is paved so wheelchair accessible. Part of it is slightly uphill/inclined. It is not a very long trail at all. I did see someone in a wheelchair when I was there so it is doable.

With a properly modified chair, one could go down the trail closer to the bridge and waterfall, but they would have to have tires sufficient to traverse dirt trails without getting stuck and be a very fit individual or have fit individual(s) assist to be able to deal with the steep incline.

The upper path yes

A small section has cement path heading to a viewing area. But the actual hike no.