I use a 4 * 1 KVM witch which accepts only 30Hz refresh rate.
How to set StartOS (via terminal on other PC) to output 30Hz rate?
Now I get only Bios start and blue Linux screen and black screen later
I don’t have the answer to your specific question. Such settings are not exposed in the StartOS interface, as servers are meant to run headless, (without monitor, mouse, and keyboard.)
The kiosk mode you see when you connect a monitor is a troubleshooting tool, which involves a browser. Browsers are notorious for memory leaks, and resource consumption. Kiosk mode only runs when a monitor is detected. Leaving kiosk mode running for extended periods of time may lead to performance issues, and system instability.