debian – Rescue system (like grml) for headless server

I am running a Debian (bullseye) server headless (no monitor, no keyboard).

Now I need to boot it using some rescue system (like grml) to do some things, that need to be done offline.

The BIOS of the server is configured to boot preferred from any usb-stick.

So I need some rescue system, that boots from usb and starts an ssh-server. I know grml has an ‘ssh’ boot option, but I have no monitor/keyboard to set any boot option. 🙁

Any ideas? TIA!