Change currency decimal separator and grouping separator for Euros

Hello r0mi, 

Thanks for reaching out to the Apple Support Communities! I see that you have a question about how to change the currency decimal separator, as well as the grouping separator for Euros. You've posted this message in Numbers for Mac, I'll begin with information for the Numbers app. 

When you're working within a spreadsheet, you can format the cells, without changing the Language & Region information on your Mac. Check out the steps under "Currency (units of monetary value)" from this article: Format dates, currency, and more in Numbers on Mac. When I tested this on my iMac (running macOS 10.15) I was able to format a cell to appear like this: €12,458,745.26.

Let me know if this is helpful. If you're looking to change the formatting for the entire computer, try restarting your MacBook Pro and then double check the steps from this article: Change how dates, times, and more display on Mac. 

I hope this is helpful.

All the best.