Lower control arm pivot nut - how do you stop the pivot shaft from spinning?

So you’re trying to take apart the suspension?

If the pivot is spinning with the nut the factory bushing is smoked. The good news is you can just disassemble the suspension anyway. Remove the torsion bar, remove the strut rod, spindle etc and the LCA will pull right off the pin.

Once the LCA is off the pin, you’ll have lots of real estate to grab onto that side of the pin to keep it from spinning.