It will usually take an impact wrench with a 1-1/16 impact socket to break that free.
You can reduce the population of sulfate reducing bacteria by cranking the WH temperature up to 140 for a while, but take steps to avoid scalding.
I put a Ceranode powered anode in to not contribute to H2S production and still protect the WH. There are cheaper ones with shorter anodes, but I think longer is better -- like the original anode rods. But even a stubby powered anode will be better than a brass plug.
I presume you are on your own well.
https://terrylove.com/forums/index....izing-extra-attention-to-4-inch-casing.65845/ is my sanitizing write-up. December-March is usually not a good time for sanitizing a well. Producing H2S in a WH takes 3 things, as far as I can tell. Sulfate. SRB. Metal ions normally from a sacrificial anode. I don't know how quickly SRB repopulates, but if you can kill off even those in the nearby aquifer, and in the WH and pipes, you will get time. How long? Not sure.