I notice now that the problem is much less serious than previously stated. The blurriness and grain seem to have been due to progressive rendering. The files are quite large and I guess while a large scan was in progress (which I stopped to produce the screenshots) the final image was taking a long time to fully render. The only thing that remains now is the yellowing. Here is an example of the expected image:
And here is what I get with tonfoto:
The yellow hue is consistent across 50 or so photos I scanned.
The camera is a Fuji X-T4 and the files are .RAF extension at about 20mb each.