as i had so many problems installing bullseye+ethercat+linuxcnc 2.9premptrt , i made this for my own future notice and a guide for others.
i used debian buster to download and make bootable flash.
downloaded bullseye iso file from here , cdimage
and using this guide, preparing files for usb memory stick booting
find flash drive name using lsblk
in terminal :
sudo apt install lsblk && lsblk
copy iso to flash and sync
cp debian.iso /dev/sdX