Translations:Install Gentoo on a bootable USB stick/49/de
From Gentoo Wiki
PROMPT 1
TIMEOUT 50
DEFAULT gentoo
LABEL gentoo
LINUX ../vmlinuz-5.10.76-gentoo-r1-x86_64
APPEND root=LABEL=GENTOO_USB_ROOT scandelay=3 ro
INITRD ../initramfs-5.10.76-gentoo-r1-x86_64.img