The arguments of the TEXT function does not work with other languages, do not use it, in 99% of all cases there is no need.
You said you changed the locale, that's the worst you can do! Reset the settings to your country as described here:
System settings - How to import a CSV file that does not match your - Microsoft Community
"2025-04-01" is not a valid date in Greek, the 1st of April 2025 should be 01/04/2025
If you imported the date or opened a file, this is not a date it's a text. Here's how to import such data correctly:
Power Query - How to import a CSV file that does not match your locale - Microsoft Community
Make a new file, write 1/4/2025 into A1

Sample file:
https://www.dropbox.com/scl/fi/zj5citiuds9a54fhj352i/55a2ad9a-1f46-4544-9e12-c0d424abcfcf.xlsx?rlkey=sunock4b9wv0cytii2ddj1o01&dl=1
All this cells contains the same date, just the number format is different for each.
The Short date is the first format of the Date formats, this date will be different on your system, because that changes due to your region settings. Same for the Long date format, which is the second format. In the screenshot above you see a German date, because of my system.
All other formats have language identifier in front and stays as they are.
If you need further help I need to see your (sample) file.
Why a sample file is important for troubleshooting. How to do it. - Microsoft Community
The article also contains a link to a macro that you can use to anonymize your data.
Andreas.