date command

Hello,

I had a raspberry pi 400 with raspbian and I changed the OS to libreelec but one of my scripts is not working. The cause is that on libreelec the date command works differently and I cannot find an article. The script uses the date xommand in this way:

$(date --date="14 day ago" +"%Y.%m.%d") but the command said that: "date: invalid date '14 day ago'". How can I get the needed date on libreelec?

Thanks.

Thanks