The problem in the original file was executing formulas
yes, this seems to be working after the fix i pushed the last time.
I tried to replicate the same issue but I am not able to perform B5=SUM(B2:B4). I have updated xlsx template. Please check.
i don't see more issues in the playground demo, i guess what you want now is to make the formulas in the Sheet1 to work, it is not throwing error now but i see the formula is defined but not producing the correct output in MS Excel (it just shows 0 as result). the reason for it to produce 0 is because you are not generating the cells with the correct number type, so when the formulas trying to do sum of cells it just find string, and when SUM is used with string it just returns 0.
you should fix the part of your xlsx transformation code to generate cells with the number type, if you have trouble with that, then just use the xlsx generation process which is designed to avoid getting into xml details about generating cells.