While commas in Number fields are hardcoded in Jira Cloud (which is what you see in the linked Jira fields of number type themselves), number formatting in JSM Forms does not currently support commas for number fields.
(As Forms used to be an external marketplace product to Jira known as "ProForma Forms" and was acquired by Atlassian in 2021, there's an understandable difference in number formatting).

Therefore, this request is to support adding commas for number data fields displayed within an active Form.