I just told you. You need to add your grub entries using "bootappend-live" in your config file or use lb config --bootappend-live to add your grub options.
This will help you understand lb config and there is also an example with grub entries:
lb config --distribution buster --bootappend-live "boot=live components username=live-user nomodeset"
It seems to me that you are new to this, my advice is that you carefully read the Debian Live Manual multiple times, because this can be quite extensive and complicated subject matter. You won't be able to succeed by simply winging it on your own or asking for a couple commands.