Hello All,
I would like to share a setting in PowerApps Portals to change the data format as per the requirement from the customer.
Create a new site setting DateTime/DateFormat in the portal and add your date format in the "Value" field. Eg: dd-MMM-yy.
If the site setting already exists in the portal, Update the value accordingly.
This setting will update all the date fields in the portal including forms and views.
Site Setting:

PowerApps Form:

Hope this is helpful. Let me know if you have any further questions
Thanks,
Mithun