Is anything other than making up that day incumbent upon someone who broke their fast in Ramadan due to a health excuse more than twenty years ago, and does not remember whether they made up that day or not?

If someone doubts having made up an obligatory day, the original ruling is that it remains a liability upon them, and they must make it up, because a person's responsibility is not discharged except by certainty of having performed it. If the delay was without a valid excuse, then a single fidyah is obligatory (approximately 750 grams of rice or the staple food of the country), to be given to the poor.