Ubuntu 20.04 on Pi 400 getting boot error "USB MSD timed out"

[/RaspberryPi]

I flashed my Pi's SD card with Ubuntu 22.04 Desktop 64 bit and it worked fine, but along the way of setting up my project found that some programs will only run on 20.04.
So I downloaded the Ubuntu 20.04 Desktop 64 bit iso (ARMv8/AArch64) from:
https://cdimage.ubuntu.com/focal/daily-live/current/
And used the Raspberry Pi Imager tool to flash the SD card. All seemed well but I got an error when the Pi tried to boot.
I wiped the SD card completely and then tried using the same iso file, but with Etcher instead, and I am still getting the same error while trying to boot, which is:
USB MSD timed out after 25 seconds.

submitted by /u/ZanyT
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