Can you use red port wine instead of regular red? How do I adjust the recipe if using port since it’s sweeter? Do I only use cardamom?

Unexpectedly, red wines can have as much or more sugar than fortified wines.
Yes, you could use port instead of red wine.
If I were making the fig jam (I've made at home but from other recipes), I'd keep all the spices the same.
Optional to keep or reduce the sugar (there is plenty of sugar already in the recipe from the fruit and the wine).