This is regression.
The last known working IoT ISO is:
Fedora-IoT-ostree-41-20241027.0.x86_64.iso

With the very same kickstart, Fedora IoT 41 does run %post sections:

# grep -irI %post /tmp/
/tmp/anaconda.log:15:59:53,292 INF kickstart.script: Running kickstart %%post script(s)
/tmp/anaconda.log:15:59:57,469 INF kickstart.script: All kickstart %%post script(s) have been run

I do not see any attempts on Fedora IoT 42. %pre section runs, though.

Reproducible: Always

Steps to Reproduce:
1. Boot Fedora IoT 42 ostree ISO with any custom ks containing %post section.
2. Let system autoinstall.
3. Without reboot, from the installer console, run:
# grep -irI %post /tmp/
Actual Results:
No relevant "%post" lines found anywhere in /tmp/* files.

Expected Results:
Something like this:
# grep -irI %post /tmp/
/tmp/anaconda.log:15:59:53,292 INF kickstart.script: Running kickstart %%post script(s)
/tmp/anaconda.log:15:59:57,469 INF kickstart.script: All kickstart %%post script(s) have been run