Uneven glow along the bottom of my 13-inch MacBook Pro screen

That one did have a repair program for some 2016 13-inch models, but it was time limited and has most likely run out by now, so go in expecting to pay. Still worth asking, they sometimes help if it was ever logged as the same fault. And back it up now. Once the backlight goes completely you're working off an external monitor.

which year is it? some 13-inch models from around 2016 had a known problem where the thin display cable wears from opening and closing the lid, and the first sign is exactly that uneven, stage-light glow along the bottom edge. it usually gets worse the further you open the lid. quick test: open it slowly and watch whether the glow changes with the angle. if it does, it's hardware and no setting will fix it. worth getting a quote from Apple or a repair shop before it turns into a dead backlight, and ask whether your model was ever covered by a repair program.