[Paladin2]

I don’t understand why a digital device that fits in the old 35mm cameras is not available yet.

[yarddog]

I think it is doable with any camera with removable backs. Probably too difficult for any camera without it as the sensor would have to be the same thickness as film.

Some of the functions could be built into the back. Probably not enough money in it.

[ThomasThomas]

I don’t understand why a digital device that fits in the old 35mm cameras is not available yet.

That is how they made the first digital cameras. Kodak made a back that would fit on a Nikon F3. 1991

You can get cameras that will use the older lens but the adapter devices just don't work good enough.