Welcome to the forum
I'm not sure what you found - perhaps you could add a reference?
I don't know if this approach adds anything, but here it is anyway.
This solution needs a "helper area" that is the same size as your actual data.
In L4 copied down and right:
Formula:
=IF(ROW() > COLUMNS($A:A)+2, OFFSET(E4, 1-COLUMNS($A:A), 0, 1, 1), "")
This moves successive columns downwards so that the cells to sum line up in a row.
The "if" prevents pulling in rows outside of the data area.
Now you can simply sum the rows of the helper area to give the result you are looking for.
The attached workbook is a subset of your data with final totals on col-C
Hope the helps.
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