Minecraft with smaller screen resolution than desktop size should fill leftover space with black

The player should be given an option, if they want to change their Minecraft Window size/resolution (in my case 3440x1440 to 2560x1440), to have all the leftover space on the sides of the window (where Desktop/Windows behind Minecraft are shown) be filled with black/custom texture (for example the dirt one for options, which can be edited with Ressourcepacks). At best that should be happening when you change the games resolution in the launcher, not while actually playing the game. Maybe this could also be an option in the videos settings menu, "Fill Empty Screen Space" or something, I honestly just need some options for having a 16:9 screen without getting distracted by my Desktop