BeamNG car has bouncy rear

That is an odd suspension setup (or very different that what I usually do…) I suggest you first get rid of the front sway bar, then make the springs and dampers more stiff, until the red and blue bars are in the line of drivability. Then stiffen the front or rear sway bars depending on what you want until you’re in the 5º to 7.9º roll degree for regular cars, or between 5 to 3 for more sporty feel (or below for an extreme race car). Then take it for a drive and tweak the suspension from there.

Also, what kind of car you’re trying to make? If you’re going for an off roader on beamng for example, get rid of the sway bars entirely and increase ride height. And as slim_jim pointed out, hover over the blue icon to get a bit of info on different setups.