An easy way is to create a Live CD version with Rufus using Windows and using persitence. There is probably some performance hit, but it works well, the only issue is the user automatically has sudo without a password, but possesion of the USB is the security itself.
It has a portable app version, but you need to go into advance settings to allow it to see your USB drives, before installation. Only 20.04+ versions of Ubuntu work with this, and during setup you need to give it your persistence size. I've used 200GB for my first test.
Author's Site Refer: https://rufus.ie/en/
Tutorial on how to Use Refer https://youtu.be/cHF1ByFKtZo
I have not tried this way because it risks messing up your host machines boot because it might put grub on the internal hard drive. It might be worth risking on an old Linux laptop but not a new Window installation.
Refer: https://www.zachpfeffer.com/single-post/Install-Ubuntu-on-an-External-Hard-Drive
Install Ubuntu on an External Hard Drive Home Zach's Blog.pdf