Hello,
The format of the date for the pivot, bar, pie is defined inside the _read_group_process_groupby method of models.py. If you need to change the format you can do it there.
I hope this will help you. I'm closing this issue unless you've got further questions ![;) 😉](https://odoo.net.cn/assets/plugins/nodebb-plugin-emoji/emoji/android/1f609.png?v=1or0p324b7t)