Inherited stock valued over $200,000. What IRS form do I file?

If you have not SOLD any of the stock, you have NO filing requirement.

If you sold the stock, the stock's basis is the STEPPED UP value, which is the value of the stock on the date of death of the decedent. In some case, the value can be on the date that is six months AFTER the date of date. Contact the estate executor to see if that alternate date was selected.

You report the sale of the stock using Form 8949 and Schedule D.

Form 3520, Part IV

IRS notice 97-34 refers to the "value of the aggregate foreign gifts". This suggests to me that gifts of cash, securities, foreign currency or even bananas that exceed this threshold value must be reported on form 3520. It is important to not overlook this requirement since the penalty for failure to report is harsh. I have always advised my clients "if in doubt, report". With all but arcane exceptions it is not taxable to you in the US.