What size threads are that fitting? Probably metric but thread pitch needs to be determined.
Or look up Dorman Line Terminator Kits 801-019 and 801-020 see if those can help.
They make these plugs for the A/C systems to block off rear A/C on dual A/C systems and other purposes.
Can be had at RA
https://www.rockauto.com/en/parts/standard+motor+products,CG7,wire+terminal,1000192
https://www.rockauto.com/en/parts/standard+motor+products,CG8,wire+terminal,1000192
What he said ^^^^^
M18 Fuel. 1000 ft. lb.
Friend has one and it's a beast but not cheap.
https://www.milwaukeetool.com/products/details/m18-fuel-w-one-key-high-torque-impact-wrench-1-2-friction-ring/2863-20