You'll need to use Raspberry Pi Imager version 1.9.x for now if you want to customise Cluster HAT images.
https://github.com/raspberrypi/rpi-imager/issues/1302
#ClusterHAT #ClusterCTRL #RaspberryPi

[BUG]: OS Customization broken for custom images · Issue #1302 · raspberrypi/rpi-imager
What happened? In prior versions, OS Customization worked for both RPi images and custom images, which was extremely handy for mildly customized RPi images (generated with pimod, for example). Now ...
GitHubIndex of /clusterctrl/testing
If you can't find a Pi4 and enough Pi Zeros for a
#ClusterHAT the
#ClusterCTRL A+6 is probably easier to fill with
#RaspberryPi 3A+
https://www.tindie.com/products/8086net/clusterctrl-a6/ClusterCTRL A+6 by 8086 Consultancy on Tindie
Network six Raspberry Pi 3A+ using USB Gadgets.
Tindie