Not sure if there is still interest in this topic but I think i got a pretty good workflow with great results.
First of all you need a light source that is very consistent in brightness as I found that changes in exposure messes with the white balance quite a bit. So better let the LED light panel warm up for a few minutes before scanning to avoid brightness shifts due to temperature changes of the LED’s.
Also it is important to shoot the whole film with the exactly same camera settings. The best practice is being in manual mode and set the ISO to 100, the aperture to 4-8 to have enough room for focus inconsistencies and better image quality in the corners and set the exposure so you get somewhere between 1-2 stops over-exposure in the meter of the camera.
Also very important is to shoot a picture of just the background light (using same focus point and aperture as for the film but faster shutter speed to avoid over-exposure without the film in place) and use this image as a flat-field image in the RAW-tab. This corrects vignetting of the ‘scanning’ lens and gives a really good brightness consistency (and white balance) across the whole frame.
You could verify this by taking a picture of an unexposed image (usually at the beginning of the film) and after Film negative conversion use the tone curve tool to move the top right white point towards the left which will blow out the highlights but shows you inconsistencies in the dark area caused by lens vignetting or uneven background light.
Next what i found, at least for my canon camera, is to use a custom Input-Profile for your camera model under Color Management in the Color-Tab. This together with ProPhoto working profile gives the best results. You can find the camera dcp profiles for many camera models here:
https://www.dropbox.com/scl/fo/h2bq18mwj5bgk3vxu5ehr/h/Camera?dl=0
Next you have to set the White Balance tool to custom and some white balance like 5000K or 6500K. Maybe you set it to your background light without film so it is neutral. The important thing is not to have camera or auto-whitebalance.
Next step is to turn off noise reduction (if it is on). This can cause some color shift (for color noise reduction) in the image due to the grain of the film which is usually bigger and looks different than noise from the camera sensor.
Turn off all shadow-highlight, tone mapping and dynamic range compression (which uses loads of CPU power for film somehow)
You can save these settings as a pre-processing profile. That makes it faster for new films.
Then either take a picture with the unexposed strip between two images to be in the middle of the picture, a fully unexposed image at the beginning of the film or take a picture wide enough to have the surrounding unexposed film in the picture. It should look now something like this:
