All datetime-like strings should use the same formatter.

[Padeanu]

On the /collections/{collection-id}/items/{item-id} endpoint, certain fields, such as assets.created or item.properties.published, are correctly formatted as UTC date strings, while others are returned as-is, resulting in inconsistencies in the date representations.

In the backend, I attempted to normalize all date values by converting them to datetime.datetime objects in Python. However, this approach does not work as expected, since the Created field in the response is required to be a string rather than a datetime object.

[m-mohr]

The browser doesn't detect that the strings are datetimes (there's no datetime datatype in JSON).
You need to make the browser aware that the fields contain datetimes.
There are two options for this:

1. Make the field definitions available in your deployment. Read more about it here: https://github.com/radiantearth/stac-browser/blob/main/README.md#additional-metadata-fields
2. Either create an extension (if your fields are resuable within a specific domain) and then submit the definitions to stac-fields

Example for the first option, to be added to your fields.config.js:

Registry.addExtension("cadip", "CADIP");
Registry.addMetadataField("cadip:planned_data_start", {
  label: "Planned Start",
  format: "Timestamp"
});