The date format in the slicer may be different from the one you are expecting if the report was created on a different computer with different regional settings. To resolve this issue, you can try changing the regional settings on your computer to match the ones used when the report was created.
To do this, go to the "Settings" app on your Windows 11 computer, then click on "Time & Language" and select "Region & Language". Change the "Format" to match the format used in the report (dd/mm/yyyy) and click "OK" to save the changes.
Another solution would be to change the date format directly in the slicer. To do this, go to the report in Power BI, click on the slicer, then in the "Visualizations" pane click on "Format" and then "Format" again. Change the "Type" from "Auto" to "Custom" and enter "dd/MM/yyyy" in the "Custom" field.
Also, check the data source, if the date format is correct or not. If the date format is incorrect in the data source, then it will be reflected in the slicer.
It's also possible that the issue is caused by browser settings, try using different browser and check if the issue is resolved or not.
