Starting from the May 2020 version of Power BI Desktop, regardless of the Windows locale settings DAX always uses standard separators by default. This change does not affect most Power BI users around the world; but if you use the comma as a decimal separator and 10,000 is just ten and not ten thousand, then you are affected by this change.
First of all, you can restore the previous behavior as I describe in this post, but the recommendation and the default are now to use the standard DAX separators. I want to describe why this (I think good) choice was made and how I contributed to making this happen.
Read the whole thing.