Can't install linux-hwe-5.8 generic-64k flavour on arm64

Found during automated testing.
Using the PPA: ppa:canonical-kernel-team/ubuntu/proposed
and the test package: kernel-testing--linux-hwe-5.8--full--generic-64k

Here's what happens when trying to install to a fresh focal VM:

ubuntu@ip-172-31-54-213:~$ sudo apt install kernel-testing--linux-hwe-5.8--full--generic-64k
Reading package lists... Done
Building dependency tree
Reading state information... Done
Note, selecting 'linux-generic-64k-hwe-20.04' instead of 'kernel-testing--linux-hwe-5.8--full--generic-64k'
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 linux-generic-64k-hwe-20.04 : Depends: linux-image-generic-64k-hwe-20.04 (= 5.8.0.45.51~20.04.31) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

ubuntu@ip-172-31-54-213:~$ sudo apt install linux-image-generic-64k-hwe-20.04
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 linux-image-generic-64k-hwe-20.04 : Depends: linux-image-5.8.0-45-generic-64k but it is not installable
E: Unable to correct problems, you have held broken packages.

ubuntu@ip-172-31-54-213:~$ sudo apt install linux-image-5.8.0-45-generic-64k
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package linux-image-5.8.0-45-generic-64k is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'linux-image-5.8.0-45-generic-64k' has no installation candidate

I could not find 'linux-image-5.8.0-45-generic-64k' in the PPA. Can also reproduce the issue by remove the PPA and adding focal-proposed.