In the presence of snapping and fractional scale, the implemented algorithm could never work correctly. The reason is that the distance between snapped positions is not the same. As a result, changing a single column width requires shifting of the subsequent or all the columns, which in turn might require a change in their widths, and so on.

This makes me think that a different algorithm might be needed, a simulated annealing perhaps.

The issue can be reproduced on Windows by setting fractional scale:

Windows 11:
Settings -> System -> Display -> Scale -> 125% (or 225% ...)

In the attached video clip, when resizing a column under AUTO_RESIZE_FLEX_NEXT_COLUMN policy, only subsequent columns should get resized.  Instead, we see that columns to the left of the one being resized are affected.  This does not happen with integer scales or on Mac.