Raspberry Pi 4 https://www.amazon.com/gp/product/B07TC2BK1X Argon One Pi 4 V2 kit https://www.amazon.com/gp/product/B07WP9P8VW SanDisk Max Endurance 32 Gb microSD card https://www.amazon.com/gp/product/B084CJLNM4
Download Ubuntu Server 20.04.1 LTS 64-bit from https://ubuntu.com/download/raspberry-pi and burn it to a microSD card with Raspberry Pi Imager 1.3 from https://www.raspberrypi.org/blog/raspberry-pi-imager-imaging-utility/ using the Select Custom option.