Some guides that may be of use: https://www.tecmint.com/install-linux-os-on-usb-drive/comment-page-5
The process described should be pretty similar with Endeavour. From what I gather, you essentially need two USB drives plugged in at the same time: one with the live ISO on it, and the other you need to format with GPARTED to install on.
I suppose the first step will be changing the booting from BIOS/UEFI onto that USB stick, which has the live ISO on it. Then wipe the second USB drive and use the installer to manually divide the blank USB between a Home (data) partition (ext4) and swap. Just select the ext4 home partition of your USB for installation then, and don’t use encryption.