Margaux, you could try to enable the Group Digits option on the property settings. (Edit page, select attribute, property pane).
Hope that helps, Thijs
In addition to Thijs’ answer, there is also the built-in formatDecimal function, or for more functionality, there is the DecimalTools module on the Marketplace that gives more formatting options if you show the output as a String.
https://marketplace.mendix.com/link/component/119981
Hope this helps.