Thanks for posting here and welcome to the community!
Can you check your excel’s formatting for the cells? You might actually have to change the format to ‘Automatic’ for excel to recognize them as formulas.
Also, maybe you have a different regional setting than me, but doesn’t the syntax use : colon instead of ; semi-colon? So, =SUM(B2:C2) instead of =SUM(B2;C2) ?
Hey, no, I already checked a lot of ways through Excel and LibreOffice Calc. Both do not work. Formulas are inserted as Text instead of as a Formula, so for Excel to recognize them you need to go inside the cell and press Enter so it recalculates the cell value and detects it as a Formula.
On SUM afaik you can use both semicolon and colon, and they do mean different things. Semicolon is like a separator, maybe you use simple commas because on some languages the decimal point separator is a comma and not a dot.
If you replace it with a colon it will have the same problem, shows as Text, n8n must be escaping it as text and not inserting as a formula or something similar.