- download ubuntu 18.04 https://releases.ubuntu.com/18.04/
- install balenaEtcher https://www.balena.io/etcher/
- install Create a bootable USB stick on macOS | Ubuntu https://ubuntu.com/download/desktop/thank-you?version=20.04.3&architecture=amd64
- put your flash memory
- open balenaEtcher - choose Ubuntu then select the flash memory