I’ve done following using buildroot-2024.08:

make raspberrypi5_defconfig
make menuconfig 
enabled rpi-userland and other RPI related tools. 
make 

Then boot from sdcard, and execute:

# vcgencmd commands
VCHI initialization failed

Stock Raspberry PI OS – works well. What am I doing wrong?

Update:

The device /dev/vchiq is missing.