I ran into this issue with Protectli devices using Coreboot and the 25.1 installer as well. I was able to get the installer working properly by doing the following:
- Spool up FreeBSD VM and attached the installer .img as a second hard drive
- Figure out which device was the .img using gpart list
- Create a directory and mount the device
- Edit the /mnt/directory/boot/device.hints and set hint.uart.0.at="isa" and hint.uart.1.at="isa"
- Un-mount the device, disconnect the .img from the VM and write it out to a USB