§ character generate incorrect output when used as function parameter string

I know, MS Access 2003 is quiet old but...

I have a stored function in my mariadb 11.4.2 server like this:

CREATE DEFINER=`root`@`%` FUNCTION `separator_test`(var_in_separatore VARCHAR(3)) RETURNS varchar(255) CHARSET utf8mb4 COLLATE utf8mb4_unicode_ci

    DETERMINISTIC

BEGIN

 RETURN concat('hello', var_in_separatore, 'world');

END

If I call this function using the ODBC connector in this way

Public Sub test()

    Dim cn As ADODB.Connection

    Dim rst As ADODB.Recordset

    Set cn = mariadbConnection

    Set rst = dammirecordset_ADO(cn, "SELECT separator_test('§');")

    Debug.Print "output: " & rst(0)

End Sub

mariadbConnection creates an ADODB.Connection object.
dammirecordset_ADO creates an ADODB.Recordset object using the query specified as parameter.

Why the output string I receive has a space at the end of the string?
Also, if I specify a 2§ as parameter the output string has 2 empty chars at the end of the string and so on.

Please note that if I trim the output string the output is always the same.
In addition, if I execute

SELECT TRIM(separator_test('§'));

the result is again the same.

I solved changing the character used as separator (using # the output string is correct) but I think there's no good reason to not use the § character, isn't it?

PS: I tried other characteres and £ character produce the same problem.

Thank you so much for your help and your effort.

Francesco