Hallo @flargo64
Welcome to the IPFire community.
Unfortunately uboot which is used to boot the arm systems does not yet work with RPi5 out of the box.
See the following post.
https://community.ipfire.org/t/ipfire-on-raspberry-5/11150/16
The wiki page shows the arm products that have been able to have IPFire successfully installed.
https://www.ipfire.org/docs/hardware/arm