Comment 2 for bug 1922779

http://cdimage.ubuntu.com/releases/21.04/beta/ubuntu-21.04-beta-preinstalled-desktop-arm64+raspi.img.xz
And config.txt looks like this
[pi4]
max_framebuffers=2

[all]
kernel=vmlinuz
cmdline=cmdline.txt
initramfs initrd.img followkernel

# Enable the audio output, I2C and SPI interfaces on the GPIO header
dtparam=audio=on
dtparam=i2c_arm=on
dtparam=spi=on

# Enable the KMS ("full" KMS) graphics overlay, and allocate 128Mb to the GPU
# memory. The full KMS overlay is required for X11 application support under
# wayland
dtoverlay=vc4-kms-v3d
gpu_mem=512

# Uncomment the following to enable the Raspberry Pi camera module firmware.
# Be warned that there *may* be incompatibilities with the "full" KMS overlay
#start_x=1

# Comment out the following line if the edges of the desktop appear outside
# the edges of your display
disable_overscan=1

# If you have issues with audio, you may try uncommenting the following line
# which forces the HDMI output into HDMI mode instead of DVI (which doesn't
# support audio output)
#hdmi_drive=2

# If you have a CM4, uncomment the following line to enable the USB2 outputs
# on the IO board (assuming your CM4 is plugged into such a board)
#dtoverlay=dwc2,dr_mode=host

# Config settings specific to arm64
arm_64bit=1
dtoverlay=dwc2