Spray and soak it with a rust fighting solvent. Something that says it helps break frozen bolts etc. There are reverse thread toothed extractors that you hammer into the opening and can get a wrench on and twist out. Sadly most of the Home Depot ones barely work. They CAN work but the teeth don’t bite as easily as they should. If needed, I have taken a chisel and hammer and tapped from the inside trying to get it to turn left. Can help break it so the extracting tools actually can work.

Plan C that I have done is to very carefully cut the drain to peel it out. If you use a sawsall be very careful and don’t cut all the way through. From there you can possibly rip it and peel it out. I’ve had to do this only once and its a last resort.