I was in a hurry. The bed plate fell on the floor. The handle shattered. I 🤬ed loudly.
Then, I remembered that Rodrigo Souza (thanks!) made a full Elegoo Mars 3 model on Grabcad.
I took the model of the handle, cut out the slot for a M10×30 hex head bolt (plus a very tight tolerance), and… voilà .
It is a very tight fit, but nothing a well tuned printer and a hammer can't deal with. Clearly, I suggest printing it on a FDM printer, but I guess you could increase the tolerance a bit and maybe glue the bolt in the slot with some more resin?
The author marked this model as their own original creation.