I have waybar set to be on the right side of my screen, but the wallpaper goes "under" it, such that if I have two windows open, the center of the wallpaper isn't in the center of the gaps between the windows, if that makes sense.
I'd like it so that the center of the wallpaper is in the center of the gaps between two windows. Or in other words, so that the wallpaper goes from the left edge of the screen to the left edge of the bar, so the bar just has a static color bg.
Open the wallpaper in your favorite image editor, crop it to the exact placement you want, add the colored border where you want it and save it into an image of the exact size of your monitor resolution so it doesn't get scaled in any way.
If you have too many wallpapers, you can also automate it with ImageMagick and a bash for loop.