Messed up External Display After Security Update

Hello all,

This morning, my Mac wasn't recognizing my external display. I tried a different HDMI port, different cable and even a different display. I decided to restart the Mac, which I don't do too often, and saw there was a security update ready, so I went on with the update. After the update was completed, the overscan on the external display was messed up and I couldn't see the status bar at the top and the screen looked much more pixelated. I'd had this issue with the other external display, but never before with this one, it just worked. Since I'd had the issue before and, for god knows what reason, there is no easy option to change the overscan on the Displays menu, I went to /var/db/.com.apple.iokit.graphics and changed the underscan value. I could get the size to fit, but the display still is much more pixelated than before, as if the Mac weren't using the full 1080p. I don't have a recent Time Machine backup, so that is not an option. Does anyone have any tips on how to go back to the old, default, "just works" setting? I'm on 10.14.6 on a 13' MBP, Early 2015. Thanks for any help!