Display Data Channel Command Interface can be used to communicate with external monitors for color calibration and brightness settings.

doas ddcutil detect

Display 1
   I2C bus:  /dev/i2c-18
   DRM connector:           card1-DP-6
   EDID synopsis:
      Mfg id:               SAM - Samsung Electric Company
      Model:                LF27T35
      Product code:         28799  (0x707f)
      Serial number:        H1AK500000
      Binary serial number: 0 (0x00000000)
      Manufacture year:     2020,  Week: 20
   VCP version:         2.0

If ddcutil is complaining about missing i2c devices you just need to load the kernel module:

doas modprobe i2c-dev

Brightness

ddcutil capabilities | grep "Feature: 10"
ddcutil getvcp 10
ddcutil setvcp 10 70

You might want to just load the module permanently:

echo 'i2c-dev' > /etc/modules-load.d/i2c.conf

ddcci-driver-linux

In addition to using the ddcutil tool directly there's a out of branch kernel module which will add your monitor to /sys/class/backlight allowing you to control it with your normal backlight tools.