On Linux there are ddcui and gddccontrol (from ddccontrol), although they probably aren't as polished as the options for Windows/macOS. There is also the non-mainline ddcci driver, which lets Linux systems manage external monitor brightness just like it would internal screens on laptops.
https://github.com/rockowitz/ddcui https://github.com/ddccontrol/ddccontrol https://gitlab.com/ddcci-driver-linux/ddcci-driver-linux