I want to know that when performing sum stacking after aligning a set of image data, if the homography transformation is used, should the stacking consider only the translation or the entire homography matrix 𝐻
The whole homography matrix is never applied on-the-fly with the stacking. Either you use sum or median or mean.
To apply homography transformation, you need to chose Apply Existing Registration to create a new sequence.
More information in the doc: Registration — Siril 1.2.3 documentation