To ISO format Which isn’t american as USA uses AM/PM dates.
Any format from here : https://www.w3.org/TR/NOTE-datetime
But in that form : YYYY-MM-DDThh:mm:ss.sTZD
The ZD is for timezone so if you have set your site as GMT+1 (= UTC+1) for ex, you’ll finish your date like this :
Wjhat happens is Webfow is going to ingest your date and convert it to UTC. Then it will convert the UTC stored date into your site date, using your timezone setting. Then in the Designer, in the CMS database and on publish, it will display the computed date in the american AM/PM format.
Edit: if you need another format I made this http://pardon-my-french.webflow.io/