How to set default date to DD/MM/YYYY ??

[TheMatrix]

Hi, i am a new user to Linux Mint(1 week old user!) and Free Office 2024. Specifically, i need to edit my MS Excel files stored in my Google gdrive across platform. I have solved the problem of syncing with Gdrive, but now i have realized my XLSX files dates has changed to numbers when i open it. How to change the default date format to DD/MM/YYYY ?

I have done the following:
1. In Linux Mint "Language" setting, "Time format" has been set to English, UK. Language is still English, US as our keyboard is US standard here. I have clicked "Apply System-Wide" and rebooted. But no difference.

2. In Planmaker, i have done the following: File->Options->Language: English(UK) and File->Options->Appearance: English (UK) as well. Nothing changes, all my dates are still in numbers. If i create a new ate cel, it always default to English (US).

How to make it DEFAULT TO DD/MM/YYYY (aka UK Date format or any other date format) PERMANENTLY? So when i opened a cross platform XLSX file, i should see the original formatting of DD/MM/YYYY?

Thank you.