Okay, maybe a Gnome Extension could help. I took a quick Look and for Zorin 18, I found 2 that You could try. But please one at a Time. Don't activate both together to avoid Issues.
For the last one, You need to install a Package called ddcutil because it lays on it. You can install it with the Command sudo apt install ddcutil via Terminal. When You look at the Link in the Comments, You will see someone who mentioned that it works on Zorin 18.1. So, maybe try this first.
To install a gnome Extension, open gnome Software and look for the Extension Manager and install it:
When installed, open it and go to the ''Browsed Tab'' and search for the Extension. then click on the Install Button. Then go to the ''Installed'' Tab where You can set it up.