I guess something like this is what I was thinking of:
https://www.amazon.com/ZhiYo-Paintable-Concealer-Management-8xL15-7in/dp/B0BW328RV8
I’m not sure if I like the idea of double-sided tape for installing it, though, since the horizontal beam has a textured surface and I’m not sure how well it would adhere to it.