Use brightnessctl and dunst to create a brightness indicator for DE-less setups

dunstBright.sh

#!/bin/bash
# dunstBright

msgId="3378455"

brightnessctl "$@" > /dev/null

brightnow="$(brightnessctl g)"
brightmax="$(brightnessctl m)"

brightpercent=$(awk "BEGIN {print ${brightnow}/${brightmax}*100}")

dunstify -a "changeBrightness" -u low -r "$msgId" \
	-h int:value:"$brightpercent" "Brightness: ${brightpercent}%"

here's something with colors and fixed decimal issue

#!/usr/bin/env bash

brightnessctl "$@" > /dev/null

msgID=31232
color="#FFBF00FF"
brightnow="$(brightnessctl g)"
brightmax="$(brightnessctl m)"
brightness=$(awk "BEGIN {printf \"%d\", ${brightnow}/${brightmax}*100}")

dunstify -a "changeBrightness" \
  "󰃞 Brightness: ${brightness}%" \
  -u low \
  -t 700 \
  -r "$msgID" \
  -h int:value:"$brightness" \
  -h string:fgcolor:"$color" \
  -h string:frcolor:"$color" \
  -h string:hlcolor:"$color"