I have tested the latest Zoneminder 1.34.26-focal2 released today and found the brightness setting is working nicely .
In earlier releases the brightness setting button did not work
Thanks for fixing brightness setting problem !

- Screenshot from 2021-04-26 17-14-18.png (351.45 KiB) Viewed 2238 times

- Screenshot from 2021-04-26 17-14-55.png (350.09 KiB) Viewed 2238 times