Apparently, the code must be updated because the external source has moved.
// Option 1
json2csv = require("json2csv@5.0.7/dist/json2csv.umd.js")
// Option 2: Use instead a file in attachment which can be loaded from
// https://cdn.jsdelivr.net/npm/json2csv@5.0.7/dist/json2csv.umd.js
// json2csv = require(await FileAttachment("json2csv.umd.js").url())