I used the following command
xrandr -q | grep " connected"
output was
XWAYLAND0 connected 1920x1080+1366+0 (normal left inverted right x axis y axis) 530mm x 290mm
XWAYLAND1 connected 1360x768+0+0 (normal left inverted right x axis y axis) 340mm x 190m
And then,
xrandr --output XWAYLAND0 --brightness 0.63
It doesn't change the brightness. These commands worked on previous machine (ubuntu 20.04). Besides the output was not "XWAYLAND0" before.
