I post this time about added "Layer mode : Alpha Diff".
"Brush mode: Alpha Diff" has the advantage of setting RGBA's A value to the larger value instead of multiplication. The advantage is that when 75% is stroked over 25%, 75% is stroked, and when 25% is stroked 50%, it does not change at 50%.
This layer mode: Alpha Diff unfortunately doesn't seem to be calculated that way. Therefore, the result does not match the brush mode: Alpha Diff.
A sample image is attached below.
Can it be improved?
After posting, the exported results confirmed that Layer mode: Alpha Diff is working properly. It seems that only the preview does not give the correct result.