Ubuntu server is not booting using the custom image option

Question

I want to install ubuntu server on my Raspberry Pi 4.

I used the Raspberry Pi imager with the image Other general purpose OS > Ubuntu > Ubuntu Server 20.04.2 LTS.

But it turns out that this image is a modified image of the ubuntu server image.
When I use uname -r I get 5.4.3-1028-raspi which is not the kernel shipped with a classic ubuntu server.

So I wanted to use the official image of Ubuntu server (the arm version).
I tried installing it on my SD card with the Raspberry Pi imager as pointed here using the Custom Image option.

But when I do that, the Raspberry Pi does not boot.

The screen says that the SD card is detected, it says Partition: 0 and retry to boot every 20 seconds. How could I make the Ubuntu Server image boot ?

Answer 1

Though the Pi is an ARM processor Ubuntu have classed these boards as IOT devices and have a specific build for them that can be found here

I would download this first then use the software to create the SD card image.

Edit: A list of supported ARM boards is here