It seems that this separator is used to separate arguments in Excel functions.
Yes, it is used to delimit arguments in Excel functions and as the default field separator when saving Excel spreadsheets as CSV files.
However, it is only used if "Use system separators" is set in Excel's advanced options (which it is by default). And this setting can be overridden with Excel's own settings.
I'm not actually aware of any other (office) applications that actually use this system setting. (Although no doubt there are.) AFAIK, LibreOffice Calc uses only its own internal settings (Tools > Options > LibreOffice Calc > Foruma > Separators > Function).
Does anyone know how to set the list separator in Mac?
AFAIK there is no explicit setting for this in MacOS. It is instead deduced from the "Decimal" setting under "Number separators" (and "Currency"?) in the regional settings. ie. If a comma is used as the "Decimal" number separator (as in your screensheet) then a comma cannot be used as the "list separator" in Excel, so will instead default to a
; (semicolon). If instead a dot (
.) is used as the "Decimal" separator, then a comma can be used as the "list separator".
This answer to a related question on Superuser.com suggests that it is dependent on both the "Decimal" settings of "Number separators" and "Currency", although it's not clear to me why "Currency" would be significant here (at least not for the function argument delimiter).