Translations:Install Gentoo on a bootable USB stick/36/de
From Gentoo Wiki
boot=/dev/sdb # The location of the USB Stick (currently)
lba32 # use lba32 addressing (ignore)
compact # boot quickly by loading lots of blocks
# remove when there are problems with booting
prompt # Prompt for user input
timeout=20 # Time to wait before default selection
default="Gentoo-352" # Default selection after timeout
image=/boot/vmlinuz-5.10.76-gentoo-r1-x86_64
label="Gentoo-352"
read-only
root=/dev/ram0
append="root=LABEL=GENTOO_USB_ROOT scandelay=5"
initrd=/boot/initramfs-5.10.76-gentoo-r1-x86_64.img