I didn’t do half those steps to stack themThe go kart has to be pushed in to the workshop before you can return it. Try bringing in an arena car with a push bumper. Then you would return the go cart if you can, then you would get in the arena car and press r-dpad to mod it, then return it. That'll unbrick it. Pull in the car you want to mod, it'll push the arena car out of the way, return the arena car, and then bring in your donor. The best donors tend to be big trucks like the cerberus and the zhaba. Good luck finding something, I haven't managed to.
But like I said I couldn’t find a merge
That’s why it’s still in a discovery section