Hi Martin,
thanks for yor proposal. Exporting with “high quality resampling” definitely takes longer, but unfortunately doesn´t solve this problem.
I found the following workaround: Switch on the highlight clipping indicator (Luminance or any RGB) and, while in “fit to screen”-view, carefully adjust details in local contrast just below the edge of clipping, set highlights to 0% and shadows to 100%. Then use a second instance and do the same … and so on until you reach your desired amount of contrast.
Not very elegant, but works.
To enhance contrast in clouds even more use the soften module with multiply blend-mode.