When using the Intel generic driver, you loose customizations made by Dell for THEIR hardware.
Install the latest driver supplied by Dell and see if the brightness controls return.
If I install the Dell driver, I can adjust the brightness, but Dell doesn't provide the latest version because the Windows Update object keeps updating itself.
Well, you have a couple of choices:
You may download from Microsoft Store the Intel Graphics Control Panel and use it like in the old driver. After installation you will find it in the Start menu, under letter "I"
Blocking driver updates in Windows is not something we support. However, you can use the procedure defined here:
Note: This link is provided for your convenience only.
If the brightness bar is missing, go to control panel, device manager, monitor, PNP monitor, driver tab and click enable. Then go back to settings - display and look for the brightness bar and adjust. ... Expand 'Display Adapters'. Right-click on the Display Adapter listed and click on 'Update Driver Software'.