Microsoft Excel can’t force comma formatting across different regions, because it relies on each user’s system locale for number formats, so it's not possible to force a certain comma style from the Highcharts side.

Reference: https://support.microsoft.com/en-us/office/change-the-character-used-to-separate-thousands-or-decimals-c093b545-71cb-4903-b205-aebb9837bd1e