when running:

aws lambda list-functions --master-region eu-west-1

the console returns:
An error occurred (InvalidParameterValueException) when calling the ListFunctions operation: The combination MasterArn=eu-west-1 and FunctionVersion=NULL is not supported. Please see our documentation for valid combinations of ListFunctions options.

Also having to use --function-version is not mentioned in the documentation.

If I run the following:

aws lambda list-functions --master-region eu-west-1 --function-version ALL

the console returns an empty array:

{ "Functions": [] } 

Seems The only way to list the functions of another region is updating the aws configuration