Do you want to use actual Debian (not Raspbian aka Raspberry Pi OS) on a Raspberry Pi? Here are the small adjustments you will need to make to an official Debian image to make it 1. boot and 2. contain some of the features you would expect from Raspbian
If you got a Free Tier VPS on Oracle Cloud and you want it to run Debian, you will not find it in pre-built OS images. Here's how you create a custom OCI image based on Debian.