If I simply replace /boot/bcm2711-rpi-4-b.dtb in the core update 160 IPFire image with one from the Ubuntu 21.10 image, IPFire boots up (if given enough time) even without a microSD card inserted. The boot up takes a long time, because u-boot expects a microSD card to be present. After some searching, the bootup finds its way to GRUB and then to the Linux kernel.
The green and red interfaces work as expected and the firewall rules appear to function properly.
However, I can’t seem to get hostapd working. I’ll start a different thread for that.
Edit: I discovered another problem – the system time is incorrect. I have a hunch that should be resolved before the hostapd problem is dealt with.