Changing comma to dot with Excel on a Mac

You don't have to change the whole language for your OS.

You can change language for Excel only, by clicking on Apps in System Preferences->Language & Region.

Also, you can just change the decimal comma to point or viceversa, without changing the language.

Click Advanced:

See if this helps.

https://www.avantixlearning.ca/microsoft-excel/how-to-change-commas-to-decimal-points-and-vice-versa-in-excel/#:~:text=1%20Select%20the%20range%20of%20cells%20in%20which,symbols%20or%20characters%20in%20the%20selected%20range.%20

As you can see in the image above, I even have two different decimal separators, one for number in general, and one for currency (euros are supposed to use comma, and I prefer period, as I am used to writing in English and that is also used in programming).

I think this will show you how to do it, https://www.howtogeek.com/240316/how-to-change-the-currency-symbol-for-certain-cells-in-excel/

Also, a great resource for these types of questions is "Mr. Excel" which has bailed me out many, many times over the past 1-15 years, https://www.mrexcel.com

Good luck.

Maybe a question for the Microsoft Product Help Communities.