I ended up fixing the issue by install RTX 3060 drivers from Del's website.
I have a G15 5515 Ryzen Edition with a GeForce RTX 3060 running Windows 10. Neither the brightness keys or the slider under Settings > Display has any effect on the screen brightness. All the drivers were current before troubleshooting began.  Here is what I tried so far, restarting the laptop after each change, but it still doesn't work. Any insight would be greatly appreciated. Thanks!
G15 5515, brightness keys and slider not working