Enabling the Raspberry Pi camera on HASSOS installations is unfortunately not as simple as connecting the camera and configuring Home Assistant as described at https://www.home-assistant.io/integrations/rpi_camera.
For the camera to work at all, an alternate firmware needs to be loaded when the Raspberry Pi boots. On Raspberry Pi OS (and many others), the alternate firmware is included with the OS installation image, and switching to the alternate firmware is accomplished by running raspi-config and selecting "Enable Camera" from the menu. HASSOS does not include either the alternate firmware or the raspi-config program, so all of the steps need to be done manually.
The steps below attempt to describe the steps that need to be performed. They have worked for me on a Raspberry Pi 3B+ running HASSOS 4.11 through 4.15. If you have a different setup your mileage may vary (but hopefully you'll get enough hints from the below to get it working).
As of HASSOS 6
