Hi,
DietPi are juts scripts on top of a Debian base image and there is no relation between the underlying OS version and DietPi version 
. In your case Raspberry OS is used as base image. Officially DietPi did not support Debian version updates but you might have a look into following link https://dietpi.com/forum/t/qbittorrent-version-shipping-with-dietpi/2326/9
Before trying to perform an upgrade, clone your SD card to be on save side !