Hi Sebastien,
I apologize for all the trouble it has caused and sorry about your time.
As per your description, you use “custom JSON to format date” in SharePoint online list but it shows different date format for different users.
May I know which custom JSON format you are using, could you please share with us screenshot it will help for us to narrow down your issue.
To change date format on a list to DD-MMM-YY, you can follow the below steps:
- Go to your list, where you would like to see the formatted date and time.
- Currently, it displays SharePoint default date and time format.
3.Now, we would like to display date DD-MMM-YY, as shown in the picture given below. We have added a new column to display the format.
4.To achieve this, we need to add a calculated column and use the sample code given below.
Meanwhile, please try to double verify Time zone setting from different user side via go to setting> site setting> Regional setting. Also please confirm does issue happen to specific list in SharePoint online or all list.
I appreciate your patience and understanding.
Best Regards
Waqas Muhammad