I tried the workaround instructions found in this thread:
But I can’t get it to work, trying to read the GPIO with both gpio and raspi-gpio it seems gpio does not manage to affect values and does so silently!?
Also “gpio readall” breaks with “unable to determine board type… model: 17” so maybe the pi 4 is incompatible with wiringpi?
Why can’t raspi-gpio set pwm?
Looking at the dependent issue maybe it never was fixed?
What about just using the brightness file in /sys/class/backlight/rpi_backlight?
Edit: You need to use the latest wiringpi on the pi 4:
sudo dpkg -i wiringpi-latest.deb