Dimmer might be worth a try.
Download it from here:
https://www.nelsonpires.com/software/dimmer
When the zip file has downloaded, click on its name (at the bottom left of your screen) to open it.
Click on Dimmer.exe to highlight it.
Click on Extract.
Click on OK.
Click the upward arrow, to the left of the address bar, to go up a level (to your Downloads folder)
Minimise any other windows (such as your browser), so that you can see the Downloads folder displayed on top of your desktop.
Click-&-drag Dimmer.exe onto your desktop.
Close the Downloads folder.
Click-&drag Dimmer onto your taskbar.
To open the app, click on its taskbar icon.
Adjust the slider to your required brightness. (It's counter-intuitive, with the setting for maximum brightness at the
bottom of the slider!)
Minimise the window to get it out of sight.
To get back to a regular display, click on the Dimmer icon in the Notification Area (bottom right corner of your screen) and close the app. (You might need to click on the 'Show hidden icons' upward arrow to see the icon).
The next time you click on the Dimmer icon in your taskbar it will remember the brightness setting you had before.
If you don't like the app, simply right-click on Dimmer on your desktop and select Delete.