How about

Intl.NumberFormat

or

toLocaleString

const number = 10000.50

console.log(new Intl.NumberFormat('fr-FR',{minimumFractionDigits:2}).format(number))

console.log(number.toLocaleString('fr-Fr', {
    style: 'currency', 
    currency: 'EUR', 
    minimumFractionDigits: 2 
}));

The display format in an apex report is determined by 2 parameters:

• Appearance > Format Mask of the column in your interactive report
• Decimal and Group separator set in the database session.

Decimal and group separator

In oracle this is determined at session level. You want , as decimal and space as group separator. To change this for your database session run the following statement.

ALTER SESSION SET NLS_NUMERIC_CHARACTERS = ', ';

• To change this for your entire application, set the following in Shared Components > Security > Database Session > Initialization PL/SQL Code

EXECUTE IMMEDIATE q'!ALTER SESSION SET NLS_NUMERIC_CHARACTERS = ', '!';

• To just set this for the page you have your report on you can either use an application process (with condition Current Page is contained within expression) = "your page" or a before header process to execute the EXECUTE IMMEDIATE statement above

Format Mask

The Number Format Models documentation might give you some clues here: 9is a NUMBER, D is the decimal separator, G is the group separator. So you're looking for 999G999G999G999D99

SELECT TO_CHAR(9866166747393/100,'999G999G999G999D99') from dual;

98 661 667 473,93

Set this as Appearance > Format Mask of the column in your interactive report.