Suggested backlight sources for scanning film with DSLR

[Digitizer]

You might be interested - or not - in a few thoughts about LED panels and diffusors.

Bright edges around 35mm Scan - What is the reason?

Had a look at your correction frame with “Digital Color Meter”, an app that comes with macOS: The frame has a falloff that ± corresponds to the bright edges in your first sample screen. The falloff seems to not be important enough for Lightroom to recognise it when you tried flat field correction…which is a pity because one would assume that FFC can also correct minute differences. According to what I found in respect of FFC, I assume that you took the reference frame with the same settings …

The generic part is below what is shown in the excerpt above…