Excel Multiplication Table Maker
Run your comments and any UI text through spellcheck. In particular, your problem statement had a few errors in it.

for number in range(1, max_number + 1):
    sheet['A' + str(number+1)].font = font
    sheet['A' + str(number+1)] = number


Is this not equivalent to:

for col in range(1, max_number + 1):
    ind = f'A{col+1}'
    sheet[ind].font = font
    sheet[ind] = col


Note that you should never call something "number". Call it what it actually does (it's a column index). Also, factor out common expressions to a variable. The same applies in your code elsewhere.

I browsed through the openpyxl.utils.cell package and couldn't find anything like this: I suggest that you write a utility function that accepts two zero-based coordinate integers and outputs a ready-to-use row/column cell reference.