To add to guidance by @Bahbus, please consider following as well
I believe there are 5 possible locale settings. Google sheets ( or back end database, Spreadhseet settings as picture shared by you), the date format of the columns in back end spreadsheet, locale settings in the AppSheet editor under Data --> Tables , the date setting of the device (mobile , tablet or PC ) itself where you are browsing/ editing the app and finally the browser locale setting.
In an app, I have all these 5 settings to dd/mm/yyyy time zones in the PC where I am editing the app. However I observe that in the detail and table view of the AppSheet editor I am getting dates in mm/dd/yyyy format as you mentioned.
However in another mobile device when I browwse that app, where I have device’s date setting to dd/mm/yyyy format, the dates are displaying in dd/mm/yyyy format in all three views.
So, in summary , I request you to once verify the date display in a different device than your AppSheet editor.
If the problem still persists, @Bahbus’s I believe workaround is a useful one or you may wish to contact AppSheet support team.